This is a (very) detailed measurements of FX-Audio DAC-X6 audio DAC and headphone amplifier. It also includes my listening impressions as usual. The FX-Audio DAC-X6 retails for just $58 shipped from Amazon: https://www.amazon.com/gp/product/B01HERNVFM/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 Comparisons will be made against Fiio E10K which retails for $78 and Topping D30 DAC ($120). See my review and comparison of those products here: https://audiosciencereview.com/foru...dslabs-odac-rev-b-compared-to-fiio-e10k.2068/ . For the second part of this review, I also include the comparison to Exasound E32 DAC ($3,400 retail): https://audiosciencereview.com/foru...xasound-e32-dac-review-and-measurements.1990/ When I was close to finishing the review, I was under the impression that this was a $120 DAC or more. Imagine my surprise where by accident I landed on its price on ebay and such and see it selling for just $58. There is no way looking at its enclosure and features that you would guess it would sell for so little money. The case is stout, heavy (for this class), and finished well. The volume control has a nice feel with notches thrown in there for good measure (kind of like a rotary encoder except that it is not).The feature set is quite rich with USB, optical (toslink) and coax S/PDIF inputs. The unit is externally powered which is another unique thing in this low price rage. As such, power consumption from USB port is minimal at 50 milliamps.Front panel buttons are old fashioned toggle switches but they have a solid, reassuring feel. There is an on/off switch which I like and a button for selecting one of the three inputs.There are two analog outputs, one line level that is fixed and the other, on the front going through a headphone amplification stage. The knob controls the level of headphone output.As is common for me these days with the latest "Creators" version of Windows 10, I test these DACs by simply plugging them in and NOT installing any drivers. This unit was no exception and it nicely got recognized by Windows allowing me to use the exclusive mode WASAPI interface to bypass Windows audio stack in Roon. Speaking of Roon, it shows the following formats supported:So darn good in that front too. Many low cost USB DACs are limited to 96 KHz, not so here.Reliability was excellent under Roon without any failures using default settings.So if you rely on that for your volume level for your system, i.e. have no pre-amp, then you can't use this DAC. Hopefully this is a firmware limitation and can be fixed.As cranky as I can be, I can't really find any faults here with the physical execution and overall functionality with the exception of volume control issue.I am going to present this in two parts. First part in this post is the usual set that you see from me. For the second part, since this DAC has S/PDIF input, I thought I use that on it, Topping D30 and Exasound E32 to run a full suite of measurements. This is made possible by my Audio Precision Analyzer controlling the source signal which is not (easily) possible using the USB port (newer versions of AP support PC control but only using ASIO and not WASAPI). To make sure the data is not overwhelming, I will put these extra measurements in follow on posts.Let's dig right in with J-Test jitter and noise test:Nothing like bad news up front. As you see in red, the FX-Audio DAC-X6 has substantially higher noise floor than either Topping D30 (yellow) or its comparably priced Fiio E10K (green). The distortion spikes are at -110 db so not a bother in practice. The noise floor though once adjusted for the way the measurements are done, will land at 90 db or so and hence, is higher than CD playback dynamic range.Next let's look at harmonic distortion using 1 Khz 44.1 Khz sampling signal:Here we see declining harmonic distortion which is good (compared to Fiio E10k) but there is a rise in noise floor proportional to frequency after 16 Khz or so.Our current champ of budget DACs, the Topping D30, delivers a big blow to DAC-X6 in this test:We have lower harmonic distortion in D30 and flat noise floor.Next let's look at ability to reproduce the lower two bits of 16-bit audio, attempting to approximate a sine wave:I don't know about you but to my eyes, there is no sine wave of any sort in the output of FX-Audio DAC-X6. It is dominated by noise and who knows what else (in red). The cyan one is from Topping D30 which takes the crown again as the best of the three.So in summary, the Topping D30 continues to outperform other DACs including the FX-Audio DAC-X6. In the three way comparison, Fiio E10K lands in the middle and the DAC-X6 easily finishes last.Story gets better though when we look at the headphone output:As we see, courtesy of its external power supply, the FX-Audio DAC-X6 has higher output both unloaded and loaded. Here is what that translates into as far as output impedance:So not too bad.I should mention that the Fiio E10 was oscillating at its peak output into my 33 ohm load. I had to turn down the volume to "6" instead of max of "8" for the loaded measurement. The FX-Audio DAC-X6 on the other hand had no such problem so measurement is at its max output.I also tested the frequency response of the headphone output:That response is very poor in high frequencies, dropping from 5 Khz on by as much as 5 to 7 dB. We should see a rule flat output. So better pair this with rather bright headphones to compensate.I listened to the line output of the DAC-X6 against the Topping D30 through my Stax SRM-007t headphone amp driving their "Pro" headphones. Going through my playlist, I could not detect any obvious differences. But if I squinted enough, I thought the Topping sounded better. See the frequency response measurements for possible reason.I then switched to headphone listening and comparing the DAC-X6 against Fiio E10K. Without level matching, the DAC-X6 easily pulls ahead. Even with level matching, the DAC-X6 sounded noticeably better with the Sennheiser HD-650. There was more bass, more clarity, etc.Switching to Hifiman HE-400i headphones, most of the differences went away. After listening for a while, I could still hear some improvement from the DAC-X6 but clearly this is a less demanding headphone than the HD-650 is. It is also more comfortable to wear.Since the Topping D30 has no headphone output, it is out of the running.Measured performance of the FX-Audio DAC-X6 is rather disappointing. It loses to similarly priced Fiio E10K and by a larger margin to Topping D30.On the other hand, its physical build is far better than the Fiio E10 and even Topping D30. And its headphone output which never gets distorted regardless of its dial position, is able to drive difficult headphones like the Sennheiser HD650.So if you want a DAC with headphone output for just pocket change, you have found it. The FX-Audio DAC-X6 provides a competent physical package, lots of inputs, and nice headphone amplifier.As a pure DAC, my recommendation remains to buy the Topping D30. Yes, it costs more but just cut back on morning coffee for a few days and you can afford it!EDIT: Hardware tear down here: https://www.audiosciencereview.com/...are-teardown-of-fx-audio-dac-x6-usb-dac.2115/