Setup and Performance

Setup

Remember when I said purchasing the SMSL SU-6/SH-6 as a combo from SHENZHENAUDIO gets you free RCA interconnects? The company was kind enough to send a set of those exact cables which are Fanmusic C003 RCA interconnects that cost $30 by themselves! These ship in a separate box and use 5 mm diameter wires, each 12 AWG33 toughened copper wires, in a 2-core configuration that gets an aluminium foil-paper shield against electromagnetic noise, and polyethylene insulation. On either end of the 25-cm cables are ROXTONE black gold-plated RF2C-BG male plugs that are gold-plated for oxidation resistance.


Despite the smaller footprint of the two devices here, the added mass of both units, courtesy the aluminium alloy stack, means that using RCA interconnects that do not have a tight bending radii will still not result in the stack tipping over. The provided RCA interconnects bend just fine although are too long to be practical if you have one unit above another as I did. These would be better used when you have the two placed alongside on a rack or even different rack compartments altogether, so I encourage SHENZHENAUDIO to consider using 10-cm long interconnects instead for the combo SKU. Given the nature of these smaller footprint units, it makes more sense to simply have one above another and I have the SH-6 amp on top of the SU-6 DAC here not only for the convenience of having the headphone output and volume knob higher up and closer in reach of your hands, but also providing more room for heat dissipation from the amplifier, which is obviously the more power-hungry of the two. Indeed, SMSL rates the max power draw of the DAC as 5 W compared to <30 W for the amplifier itself! I will also say that the inner heatsinks and aluminium chassis make for a setup without any heat-related issues, even over longer sessions. Both units also have a standby power consumption of under 0.1 W, so you can leave them running in idle when not in use. The minimum amount of cables to be connected for the stack thus involve both power cables, the RCA interconnects, and the input connection to the DAC. I have used the provided USB cable as well as connected the Bluetooth antenna in the photo above. You may also want to consider the pass-through option to use the stack as a preamp headed to active speakers, and using a mobile source is also possible if it supports USB OTG.


Powering on the stack now shows off the display on the SU-6 DAC as well as the lit indicator LED in the SH-6 amp. For the purpose of this review I will mostly focus on the DAC here since that is where your eyes will be naturally drawn to for relevant information. I appreciate the white (slightly warmer white) color used for the display here behind the tempered glass panel, and it's quite sharp too while also giving actual brightness control that I didn't realize I needed on such units until now. What I don't appreciate as much is the limitations on the text to where some can be hard to interpret if you were not already expecting it. The "bt" indicator is a good example of this, and you can press the capacitive button to cycle through the inputs or simply use the provided remote control.


The display does come in handy to show the current input mode as well as playback rate, as seen above where it defaults to 32-bit, 44.1 kHz PCM playback in Windows. The actual bit-rate is not seen here though, but you will get DSD playback indication when it's active. The stack is also set to max volume by default, and here you do need to use the remote control to make use of the stack as a preamp or for volume control going down to -99 dB.


Using the SMSL SU-6/SH-6 stack with Windows 10 or 11 doesn't require any additional drivers, with Windows recognizing the device automatically. We see that the default firmware provides PCM playback options up to 32-bit, 384 kHz. The XMOS XU216 USB encoder microcontroller comes in handy here, and all your favorite players will recognize the device in WASAPI (Windows Audio Session API) mode accordingly. There should be equivalent drivers pre-configured in newer macOS builds too, but I am not familiar enough to speak on this front. The SU-6 also allows Bluetooth pairing with phones/laptops/desktops and even supported TVs with Bluetooth 5.0 and SBC, AAC, aptX adaptive, and LDAC support, which is a welcome surprise given that the specs sheet only mentions aptX HD as the best codec supported! Indeed, the display goes from aptX to LDAC on the screen, so this is perhaps a case of SMSL needing to update its product specifications, given that there is no firmware update possible.


If you have a device that doesn't accept UAC 2.0, or simply want to try other options, then the generic XMOS USB audio device drivers will be of interest to you. You can find the installer on the product page and the latest version at the time of testing was v5.50.0 from Sept 2022. Installation is trivial as seen above, and these drivers now allow you to make the most of the SMSL stack within the Windows operating system.



What these drivers do after installation is create a new output device in Windows, also providing access to the XMOS USB DAC Driver Control Panel. SMSL did not bother to re-skin these drivers with a new name or device ID, as with the likes of FiiO and TOPPING, thus we only get the generic "SMSL USB Audio" device identifier here. Not that it really matters, given you only use it in newer Windows builds if you want to have the stack as an ASIO (Audio Stream Input/Output) device. Set the format to your choosing and choose the buffer size based on latency requirements. With that done, go to your media player of choice. I demonstrated above with JRiver again and set the audio player to the same output. At this point, you can implement further tweaks, but those are player dependent. These drivers also provide 16- and 24-bit playback support as seen above. Interestingly, JRiver also provides a direct sound option here, unlike on the previously covered XMOS-based ASIO solutions.

Audio Performance

Here is an example setup with the HIFIMAN HE1000se planar magnetic headphones, as well as the MOONDROP Aria Snow Edition IEMs connected to the SMSL SU-6/SH-6 stack via the 1/4" single-ended headphone output on the amplifier. The IEMs necessitated use of a 3.5 mm to 6.35 mm (1/4") adapter and thus I noted the absence of an included one with the SH-6, and these two use cases help illustrate the broad application of this DAC/amp stack, given the vast difference in cost and power requirements. Indeed, the HE1000se costs 10x the asking price of this stack, and yet gets plenty loud off the SH-6 that can provide up to 2.6 W per channel at 16 Ω going down to 1.3 W at 32 Ω. This is on high gain mode though, so your mileage may vary as to using this stack for more power-hungry headphones—especially if you are a proponent of keeping gain low. Here the SH-6 amplifier shows some shortcomings compared to the likes of the TOPPING L30 II that has not only more maximum power, but also more gain control too, making it a more effective amplifier for different use cases. I also thought the HE1000se wasn't getting as dynamic here as with better amplifiers and I did not notice it with the L30 II as much. Low gain mode on the SH-6 works well for IEMs as well as most consumer headphones and the ultra-low output impedance combined with the useful volume control over both DAC and the amp (with the volume knob) come in handy here. Overall I do think the stack has a stronger DAC than amp, with more current-demanding scenarios pushing it beyond its strengths.


As with most such linear amplifiers, the SMSL SH-6 amp is acoustically transparent. This means the sound signature of your headphones, IEMs, and speakers will not be changed when driven through the amplifier at least. Indeed, I dare say this is all you could ask from a headphone amplifier, unless you are deliberately looking for a colored sound signature, and I mentioned above how it's suitable but not necessarily the best amplifier you can get, even in this more budget-friendly price range. It's actually the SU-6 DAC that is the star of this show with excellent measurements as well as nice features for the money, as previously pointed out. Keep in mind that the SU-6 does follow a typical ESS Sabre DAC implementation in being clean and flat, and this is really all I can ask for in a beginner stack/DAC. It's nothing new and yet I measured a flatter response without any coloring than even some of the most expensive DACs tested to date! I'd easily place it as a better overall DAC compared to the TOPPING L30 II and possibly also the L50, and certainly more so than the JDS Labs Atom DAC+.