"Incredible": Joshua Valour Reviews the FiiO K9 Pro DAC/Amp

Note: This article is based on the video "DMS recommended this amp! Is it any good!?" made by Joshua Valour on his YouTube channel and is printed here in partnership with Joshua Valour. The review was originally posted on January 17th, 2022. Edits have been made for clarity and length.


What’s up, guys. My name is Josh, and welcome to another video. Before we get started, Apos Audio sent this out to me. FiiO has nothing to do with this review, and no one is paying or asking me to say anything good or bad.

Let’s start off with the warning label, because this has got the biggest warning label of any audio product I think I have ever come across. It’s just for the voltage switch on the bottom of this unit, but it’s huge. 

The build

The build itself is dense. This is worth every bit of the $799 asking price. This is one dense unit. Not only is the density very high, but the actual build quality in general is much higher and greater than any other FiiO product that I’ve personally ever looked at. This thing is actually pretty impressive. Not only is it impressive for a FiiO product, it’s impressive as a general audio product in this price category. It’s really well put together. 

The FiiO app

You’ve got a ton of inputs and outputs. This thing is pretty flexible, and it can also handle a number of Bluetooth codecs, which you can select in the app. Yes, there is an app. The app has control over almost all of the functionality on this device. It can cover things from the ring light being off, blue, or an RGB gradient. It can control the brightness of the light. It can change your input source remotely from your phone. You can change the Bluetooth codec. You can do channel balancing and DAC filters, and there is an equalizer. I’ve only been able to use the equalizer with Bluetooth, not when I’m plugged in via USB or optical, unfortunately. I’m not sure if this is designed that way or if this is a glitch in the app. 


Now, one of the stranger things that I’ve come across with this thing is that there is a USB-C port on the side of the device. On the website, it says that this is for smartphones, but I could not get it to connect to either of the iPhones that I have.

Notable quirks

Now, this build is generally very good. It’s super versatile. I like the app support. I like the input selection and output selection. This basically covers anything most people will want, but there are a couple of quirks that I think are noteworthy or just straight up not that great.

One of the noteworthy things is that when you switch devices, say from USB to Bluetooth, it will unconnect the USB from your computer, so all of a sudden your computer will default to whatever is the default audio device. Once you switch it back to USB, it will then reconnect to your computer, and it doesn’t stay there as an available source on the computer all the time. Now, like I said, depending on how you run your setup this could be a good or bad thing. For my setup, this doesn’t really work all that well. I don’t like it too much.

Another feature of this is that you can tell this sounds good because it’s got a gold sticker on it. Oh, wait, Josh, it’s not actually a gold sticker. It’s actually a plastic built into the chassis that you cannot get rid of. I don’t know why. Sorry.

One actual complaint that I have about the build is that the buttons and switches on the side are kind of difficult to see. Now, you get around this eventually just by muscle memory. 


This features technology that we’ve seen in many other amplifiers, which is THX technology. This specifically uses the 788 plus. Now, this has been paired with an AKM4499EQ DAC chip, and the combination of the two does seem to be a winning recipe. We did see the 788 plus in another DAC/amp before, which came in at about $500, but has since been discontinued. I personally like the sound quality of this one a little bit more. It’s not quite as flexible in the EQ realm, but it does have a lot more input options, including things like Bluetooth, and the build quality is just substantially better. This DAC will handle up to 384kHz, DSD, and MQA, for those of you who are into that. 


This amp measures fairly well. The total harmonic distortion for the entire system is about 0.001%, so it’s very low, though not the lowest. I think at 32Ω it will output 2 watts. It’s definitely not the most amount of power for the money. Like, if you were to split this up into a stack you could get more power and even cleaner specs, so with this I think the appropriate way to look at it is not as each spec mattering as much as necessarily the complete picture, and seeing if that completed picture fits your particular lifestyle. 

Sound quality

The top end is slightly quenched on this, slightly more liquidy, smoothed-over. A little bit more milky than something like a THX 789, for example. Now, this amplifier is still a specific-sounding amplifier. It’s still very exact and precise-sounding, but not quite as much as the 789. It’s a little bit smoothed off in the top end–not a ton but a bit. This will do a fantastic job of cooling down some more energetic headphones, but you may prefer the slightly more clinical sound of the THX 789. Now, I do very much agree with the tonal changes that DMS mentioned. The Monoprice THX DAC/amp, by comparison, seemed tonally bottled to me. You could adjust it with some EQ, but by comparison the FiiO seems a lot more open and free and forgiving for tonal properties. It seems a little bit warmed up compared to that. It seems a little warmed up from the otherwise sterile tonal properties of a lot of the THX stuff that I’ve heard. Now, the bulk of this sound is very THX. It has the brand’s house sound, which is fast, clear, domineering, over-imaging, dynamics, and bass response, with an incredibly deep blackness in the spaces between instruments. 


So in conclusion, this thing has a couple of weird quirks that I would personally change; however, altogether, this is an incredible amplifier with a very wide feature set, a great build quality, and a sound quality that is absolutely worth the asking price. Another great recommendation from DMS.