Scroll down and see that Editor's Choice award, and keep in mind that this is only the second time I have given it out in the audio/headphones category. The first was with a then-impressive tribrid driver set of IEMs that certainly would not receive it today given the experience I now have with IEMs and headphones. It could thus be argued that the FiiO K9 Pro ESS benefits from it, too. The feature set here won't really diminish over time; if anything, it will only get better with firmware updates. This is already an iterative release based on a successful product, with the update forced due to literal DAC chip shortages. However, FiiO also improved the user experience with a more fleshed-out accessory set and increased customization options in the mobile app.

Incidentally, I really liked the Bluetooth connectivity. There's something to be said about relaxing on a couch with your favorite headphones and no worry about a really long cable from the headphones to the K9 Pro ESS or the latter to the source. Of course, the sound signature won't be nearly as clean or detailed as from a wired source to the K9 Pro ESS, but it effectively makes the K9 Pro ESS a beefed-up version of the BTR5. App support is similar too, and includes easy 10-band EQ where needed. I acknowledge that some would prefer a remote control over the app, but I prefer the mobile app as it keeps things simple without an additional item taking up room. Add all the codecs you'd ever want, including LDAC, and I hope I am making a strong enough case for owners of the K9 Pro ESS to at least consider line-of-sight Bluetooth transmission.

For most others, the K9 Pro ESS is a reference book in getting the basics right and going a step or two beyond. There are plenty of input and output options to meet most needs, and I really have no complaints on the sound quality. Noting that DAC/amp combo units tend to cost more than separate stacks, I also see impressive scaling in the feature set and overall output going from the $200 K5 Pro ESS to this, but not as much as with the JDS Labs Element II which slots in between the two price-wise, but has been overtaken by the newer OLED-equipped Element III. In fact, I am going to replace the Element II with the K9 Pro ESS for more demanding headphone testing and frequency response measurements since this is a transparent source I just need to have two wires from. The internal power supply is also appreciated, especially as the partitioned PCB design gets around any signal distortion. While it's not perfect and there remain some things I'd change, the overall pros lists heavily outweighs the cons. I can see why the K9 Pro ESS received so many glowing reviews, and it now gets to add another one to its tally!