FiiO K9 Pro ESS review: desktop DAC action

Since starting out in 2007, FiiO has been moving carefully but determinedly up-market - but without ignoring the entry level where it established its reputation in the first place. ‘Up-market’ where desktop-friendly headphone amplifiers/digital-to-analogue converters are concerned means this: the K9 Pro ESS.

Its specification is extensive, its functionality and compatibility wide-ranging, and its build quality gives every impression of being good enough to survive even quite sizable detonations. But is it any good? That's where this FiiO K9 Pro ESS review comes into play...

FiiO K9 Pro ESS: Price & Availability

The FiiO K9 Pro ESS headphone amplifier/DAC is on sale now, and in the United Kingdom it’s priced at £699. In America you can pick one up for $849, while in Australia you’ll have to part with AU$1349.

It hardly needs saying that this is proper money for a desktop-orientated headphone amp/DAC. And yet it’s by no means your only choice at this sort of money among the best DACs - we’ve heard and enjoyed similar (and similarly priced) products from the likes of Cambridge Audio, Chord and iFi. So there are strong benchmarks to test the K9 Pro ESS against…

FiiO K9 Pro ESS review: Features & What's New?

As seems only reasonable in a product like this, especially one that costs this sort of money, the FiiO K9 Pro ESS is thoroughly specified and incorporates more complex abbreviations than you can shake a stick at. 

The actual business of converting a digital audio signal to an analogue version your headphones can deal with its taken care of by two ES9038PRO DAC chips - one for each of the stereo channels. The signal’s amplified to the point your headphones can make sense of it by a couple of THX AAA 738+ chips - they’re powerful enough that no pair of headphones, no matter how tricky to drive they might seem on paper, is off limits.

The FiiO uses an over-sized linear power supply with a low-frequency transformer and four hefty capacitors to deliver the power its audio architecture needs. To keep crosstalk and signal degradation to an absolute minimum, the PCB is laid out in a balanced configuration, and is partitioned to keep both the audio signals isolated from the power supply and the analogue signal loop fully independent too.  

Getting audio information on board in order for the FiiO to do its thing can be done a number of ways. On the rear panel there’s a USB-B input (good for file sizes up to 32bit/384kHz and DSD256), a digital coaxial (24bit/192kHz) and a digital optical (24bit/96kHz). Line-level stereo RCA ins and outs are here too, along with a super-serious pair of balanced three-pin XLR outputs and a 4.4mm balanced input. Balanced 4.4mm and unbalanced 6.3mm headphones sockets sit beneath a balanced four-pin XLR output. And on one of the sides of the chassis there’s a USB-C socket just for good measure.

The rear panel also has a post for a Bluetooth aerial (the aerial itself is supplied in the packaging). The wireless show is run by a Qualcomm QCC5124 chipset, and there’s Bluetooth 5.0 with SBC, AAC, aptX HD, aptX Adaptive and LDAC codec compatibility.

FiiO K9 Pro ESS review: Performance

When you hard-wire the FiiO K9 Pro ESS into a system - whether that’s via USB-B to a laptop, via digital optical to act as a DAC for a CD player, or via its analogue stereo outputs in order for it to become a preamp - its overall attitude and sonic characteristics don’t really undergo much of a change. It’s a swift, manoeuvrable and prodigious detailed listen, and it’s ready to let you have a full and explicit picture of whatever you’re listening to.

With some properly high-resolution content coming aboard via USB-B and a pair of appropriately talented headphones plugged into one of its balanced outputs, the K9 Pro ESS is capable of remarkable insight. Detail levels are impressively high, as is the deft way the FiiO contextualises even the most transient, minor occurrences in a recording - this is no dry tool of analysis, it just doesn’t let any information go astray. The K9 Pro ESS’s overall presentation is unified and explicit, certainly - but it’s also musical and entertaining.

It’s particularly adept through the midrange. Singers get every chance to shine - they have plenty of space on the big, well-defined soundstage in which to operate, and every last drop of their technique, their attitude and their power of communication are expressed. The tonal balance here, as at the top of the frequency range, is neutral and natural - and the low-level dynamic variations apparent in every singing voice are served up just as readily as the broad aspects of performance.

Really, it’s only at the bottom of the frequency range that the FiiO doesn’t sound entirely confident and positive. The same sky-high detail levels are here just as surely as they are elsewhere, and the control the K9 Pro ESS demonstrates means it fairly snaps into and out of bass sounds. There’s good extension, and great variation where texture and tone are concerned. But the FiiO just doesn’t have a great deal of low-frequency presence - the bass it produces is properly realised, but it’s short of weight and substance. It’s not difficult to imagine any number of listeners hankering after greater ‘punch’ than the K9 Pro ESS is willing to deliver. The rapidity of its low-end presentation gives great rhythmic expression, but ironically it doesn’t make the FiiO a great dancefloor proposition.

Switching to Bluetooth with the K9 Pro ESS acting as receiver can impact on those detail levels just a little, and there’s a small knock-on effect to the clarity of the soundstaging too. But the FiiO remains poised and engaging even when used (partially) wirelessly, and is certainly less grumpy about this sort of functionality than some alternatives.

FiiO K9 Pro ESS review: Design & Usability

In all honesty, not a lot of what you’d call ‘design’ has gone on here. FiiO has specified some high-quality, tactile aluminium and then built a chassis out of it - and that’s about the extent of the designing that’s gone on. Unless you count either the subtle little angles along the top edges of the box or the unsubtle gold accents around the big central volume control, anyway. And to concentrate all the visual interest in the centre of the fascia, FiiO has surrounded the volume control with a ring of light - the colour is dictated by the standard of the incoming signal. 

At 70 x 200 x 22mm (HxWxD) and 2.75kg, the FiiO is one of the bigger and bulkier examples of its type. It’s small enough to sit on your desktop without requiring a huge rearrangement of your possessions, though, and if you want to use its preamp abilities in a full-size system it won’t hog too much shelf space. And FiiO provides a little stand in the packaging, so you can position your K9 Pro ESS on its side if you prefer.

Once it's in position, the K9 Pro ESS is easy enough to operate. Its inputs and outputs are all sensibly spaced, for starters, so making physical connections is no hardship. The few physical controls on the fascia, next to the volume control, are simple too - there’s a three-position switch for output (DAC, preamp or headphones) and a similar switch for gain (high, medium or low). A button lets you cycle through your input options (and lights up a confirmatory LED), and there’s another button to mute/unmute and to either wake the K9 Pro ESS or switch it to ‘standby’.

There’s also the FiiO Control App, which is a clean and stable example of the type. As well as confirming the standard of the audio signal the machine is dealing with, it allows you to adjust EQs, audition a selection of filters, check for firmware updates, specify the Bluetooth codecs you’d like to access and so on. It’s free for iOS and Android.

FiiO K9 Pro ESS review: Verdict

In some ways - the thoroughness of its specification, the aluminium build - the FiiO K9 Pro ESS goes above and beyond. 

But unless you’re pairing it with some very bass-happy headphones, its sound is fractionally lightweight and lacking low-end body. 

In every other respect, though, there's an awful lot to recommend the FiiO K9 Pro ESS - both in the way it sounds overall and where its functionality is concerned.

Also consider

The Cambridge Audio DACMagic 200M doesn’t have quite the suite of connectivity the FiiO K9 Pro ESS does - there’s no balanced inputs or balanced headphone output, and it doesn’t have quite as wide a range of Bluetooth codec compatibility either. But it’s usefully cheaper, can go all the way to 32bit/784kHz and DSD512, and is mercifully short of gold accents in its design.