Introduction

This is the second in a series of FiiO products being covered on TechPowerUp, with the first the FiiO FA7s set of all balanced armature driver in-ear monitors. I mentioned in said review how FiiO puts out more products in a year than most companies do in a decade, and FiiO not only has multiple lines of IEMs, but various sources to drive them in the form of digital audio players and DAC/amp combo units. We have previously taken a look at two separate FiiO portable DAC/amps, covering both wired and wireless options, and now examine a desktop class unit in the same realm.


The FiiO K5 Pro ESS is a forced iterative release due to the AKM factory fire of 2019, which resulted in a massive shortage of digital-to-analog converter chipsets from arguably the biggest manufacturer of said chipsets at the time. ESS quickly saw growth opportunities galore and expanded its Sabre DAC line to cater to the demands of all of AKM's customers left helpless for future plans. As the name suggests, the K5 Pro ESS uses an ESS DAC and is otherwise similar to the older K5 Pro desktop DAC/amplifier that distinguishes itself from the portable class by necessitating AC mains as opposed to USB power. The original plan was to combine coverage of the K5 Pro ESS with the FiiO FA7s IEMs akin to the FD3 and New K3 from before, but it quickly became obvious that the FiiO K5 Pro ESS is worthy of its own article. Then another FiiO item came along and bumped the K5 Pro ESS off a dedicated review slot, so we are at it with a detailed quick look article instead! Let's thank FiiO for providing TechPowerUp a sample as we begin with a look at the product specifications in the table below.

Packaging and Accessories

I could write a whole page dedicated to FiiO's packaging and it would still fall short, such is the nature of the great first impression FiiO products leave. The K5 Pro ESS comes in a thick cardboard box with a black base and glossy iridescent printing that changes color depending on the viewing angle and that of incident light. On the front is the company logo and product name along with an outline of the product and its salient marketing features. Some basic specifications are on the back, accompanied by contact information for FiiO and an interesting note about the product likely going to be upgraded—I don't know whether this was before the K5 Pro ESS was even a thing outside of that label on the bottom. Side flaps on top can be unfurled to access the contents inside, with the K5 Pro ESS safely placed between two shaped foam sheets, a handy user manual on top (online copy here), and the other accessories inside a separate smaller cardboard box at the bottom.


I mentioned that the FiiO K5 Pro ESS is a desktop class source, and with it comes a two-piece AC mains power adapter and power supply that accepts 100–240 V and up to 0.55 A while providing up to 22.5 W on the 15 VDC rail. Additionally, you need a USB connection to make the most of the product as an actual DAC, and FiiO provides a 3' long Type-A to type-B cable, no doubt for a USB type-B port on the K5 Pro ESS itself. A warranty card completes the paperwork, and we then see a 3.5 mm to 6.35 mm (1/4") single-ended adapter to convert IEM/portable headphone cables to the larger output on the FiiO K5 Pro ESS. Rounding off the unboxing section is a dust cover for an optical input, and a set of four circular rubber feet.

Closer Look

Having recently used the FiiO New K3 for a couple of IEM reviews, I went in expecting an aluminium alloy enclosure in a matte black finish that feels and looks cool in person. I still was not expecting the K5 Pro ESS to be that much larger at 120 x 146 x 55 mm and weighing nearly 500 grams. This is a solid-feeling chunk of metal, which is reassuring in a manner that doesn't mean much by itself, but is good nonetheless. The design language is clean, with tasteful branding on the top and the Hi-Res Audio logo showing up twice. Smooth, rounded corners greet us, as well as a front fascia that distinctly curves outwards for some glitz to an otherwise monochrome design. On the front, from left to right, is an input selector switch (1- USB, 2- Line in, 3-SPDIF/optical) alongside another switch for low to medium to high gain via an increasing number of filled dots. These are steel switches with good tactility and no room for ambiguity on where they land. The center is occupied by a relatively large volume knob that also acts as an on/off switch at the starting position, and there is a painted-over line to show current positioning. Then comes the expected 1/4" (6.35 mm) single-ended headphone output on the right, and as shall be seen later on, an indicator light is associated with the volume knob.


Various supported inputs on the back are neatly labeled as such, with the numbers corresponding to the three on the input selector switch of the front. Going from left to right, we get a choice of either Coaxial or S/PDIF for a digital signal to the output, corresponding two-channel line in and line out RCA ports in white (left) and red (right), and the undoubtedly more often used USB Type-B input to use the FiiO K5 Pro ESS as a proper desktop source—the more relevant application for TechPowerUp readers. The power jack is all the way to the right, and further branding and certification information is on the top and bottom alike. An examination of the bottom reveals four pre-installed rubber pads that raise the K5 Pro ESS off the desk to prevent scratches to the metal chassis while adding friction against the desk, so the provided replacement feet in the box could be used when the pre-installed ones wear out or to lay the K5 Pro ESS on the side if desk space is limited.


At this point, I was about to show you some photos of the insides of the K5 Pro ESS—after all testing had been finished, of course. However, a single stripped screw head destroyed that endeavor. Instead, I decided to treat you to a family photo session of the FiiO K-series of products I have on hand, including the portable New K3 we saw before, this K5 Pro ESS, and the newer K9 Pro ESS, which will have its own full review and is why the K5 Pro ESS got a quick look article instead. If you were wondering what makes this a K5 Pro ESS and what happened to the K5 and K5 Pro, I'll refer you to this handy FAQs section that describes the exact differences between these models. In summary, the K5 Pro with an AKM AK4493 DAC added some more features and fully replaced the older K5, and the newer K5 Pro ESS has the ES9038Q2M DAC with slightly better performance. Note how the K5 Pro ESS stacks up in the middle of the three quite well in both size, mass, I/O options, and no doubt cost!

Usage and Audio Performance

Using the FiiO K5 Pro ESS is as simple as deciding upon your audio input and connecting the power cable, with my preference the USB input from my desktop or laptop. There is no dedicated on/off switch; instead, you will use the switch integrated into the volume knob on the front that clicks on and provides visual feedback with a ring of LED lighting around the volume knob. The knob cover plays a role in light distribution, including in the sharper top-down cone at a more extreme angle, when the volume knob is close to zero or maxed out. By default, you would see a blue light when powered on and an input is detected, which is the case with PCM playback up to 48 kHz. It then turns yellow past 48 kHz or green with DSD playback, and red when there is no audio input. These four colors identify the operating state of the audio chain, and help troubleshoot any faults. Connecting the K5 Pro ESS to your desired output is also quite simple as there are only two options: line out to, say, an active speaker or dedicated amplifier, which would have the FiiO K5 Pro ESS act as a preamp/DAC, or the 6.35 mm headphone out on front. Both are viable options for a desktop setup with speakers or headphones and IEMs, with the provided 1/4" adapter coming in handy if your preferred set has a 3.5 mm cable instead.


Given I could not easily disassemble the device, I instead relied on FiiO to confirm the use of an ESS Sabre ES9038Q2M—a 32-bit low-power version of the higher-end ES9038 chip that made waves a few years ago and continues to be used today. This is a reference-class stereo USB DAC meant not to add any coloring to the sound signature, and it is the exact same DAC as in the portable-class FiiO New K3 we saw before. Based on the similar configuration, I am also inclined to say the USB encoder is an XMOS U30881C10, which is the commercial variant of the XMOS XUF208 32-bit microcontroller handling the USB input. It is capable of decoding up to 768 kHz/32-bit files and 512-bit DSD files natively and converts USB audio into digital signals that are then passed onto the DAC. Where the K5 Pro ESS separates itself from the New K3 is its dedicated amplification platform consisting of a Texas Instruments OPA1642 operational amplifier and a TI TPA6120 headphone amplifier. It has the K5 Pro ESS provide a whopping ~1.5 W of clean power at 32 Ω impedance, albeit at high gain and with the volume knob maxed out. So it can get pretty much any set of headphones loud enough, although there isn't a lot of headroom with low sensitivity planars. I am not going to use it to run the HIFIMAN Susvara, for example, although it did work plenty fine with the recently covered dynamic driver headphones, such as the HarmonicDyne Zeus, Sivga Phoenix, and Sivga Robin. With IEMs, it's arguably too much power even at low gain, so much so that the output impedance needs to be considered. I tried and failed to drive some ultra-low impedance IEMs without any background hiss or distortion at audible volumes since the K5 Pro ESS has an output impedance of 1.2 Ω, but it was the only time I felt the lack of a black background in use. This is otherwise a capable device that is mostly plug and play—some quick EQ options would have been nice, such as the bass boost switch on the new K3. Additionally, there is no toggle to select between USB audio class 1 or 2, which is handy for use with some older inputs, and game consoles.



Using the FiiO K5 Pro ESS with Windows 10 or 11 doesn't require any additional drivers, with Windows recognizing the device automatically and arguably providing all the playback options the average end user will ever need. But of interest to audiophiles will be the Audio Stream Input/Output (ASIO) drivers, the installer of which is available here. The latest version at the time of testing was 5.30.0, and these allow you to make the most of the FiiO K5 Pro ESS in wired mode. An online guide goes over the installation and setup of the generic FiiO USB DAC drivers for Windows. Be sure to set the format to 32-bit and choose the ASIO buffer size that suits your latency requirements, and that's about it.


What it then does is create a new output device in Windows called FiiO Q series you want to set as the default before configuring the desired bitrate, and playback rate via the XMOS XUF208 USB microcontroller/decoder with asynchronous USB Audio Class 2.0 decoding. Notice the additional 24-bit options you now get, which some may find useful. With that done, go to your media player of choice. I demonstrated above with JRiver and set the audio player to the same output. At this point, you can implement further tweaks, but those are player dependent, so I will not talk about them too much by having the photos above speak for themselves. I also deliberately choose the ASIO driver as the output to show its options, but of course went back to the FiiO Q series output to have the K5 Pro ESS running properly in USB DAC mode.


I spent a long time using the FiiO K5 Pro ESS with a variety of headphones and IEMs, although I did test the line out features briefly if only to say that the line out works as expected. This is a source best paired with headphones I felt, although low gain and a careful hand on the volume knob can get you going with most IEMs, too. I did not notice any coloring of the sound signature, but measured it to be sure. To do so, I used a few different headphones and IEMs and measured their frequency response from a known transparent source to then compare those when driven off the K5 Pro ESS. Notice the scale bar on the Y-axis—you want a flat 0 dB line from 20 Hz to 20 kHz to match expectations, which is what we have here.

The FiiO K5 Pro ESS sells for $199.99 with the power plug of your choice from the FiiO Aliexpress store, and from authorized vendors, including HiFiGo as of the date of this article. It's an excellent set that also measures very well if you take the first-party data for granted, and in the absence of an expensive audio analyzer, there's not much else but to relate that my subjective experiences coupled with the flat sound signature have all been impressive for the money, knowing that a typical ESS Sabre DAC-equipped solid-state amplifier is a working formula. This is good value for the money with minimal compromises, making it a good choice for those looking for a desktop DAC/amp that can easily fit under a monitor and provide oodles of clean power, though there is the distortion-related ESS hump to consider, of course. It also comes with dedicated ASIO drivers and all the PCM/DSD playback support one could want. There is no MQA rendering though, which is a positive in my books since it kept the cost of this iterative release at an even $200!