I had a Aune X8 here for testing against a Topping D50s. Musical Fidelity V90 was here for reference (long term DAC). The X8 has a lovely volume knob but the sound was somewhat thin vs the Topping D50s, when using both of them as DAC/pre-amp. Vocals on the Musical Fidelity V90 beat had less grain than either of these, albeit the MF V90 must be used with a pre-amp in front of it. The V90 doesn't go higher than 96 kHz and doesn't do DSP. Neither of those really matter to me, although I've had some pleasant experiences with a Topping E30 at 384 kHz PCM. The E30 doesn't suffer from the same grain in vocals (yes I listen to a lot of vocal music). Have considerable difficulty picking a favourite between the E30 and V90. Both have a wider soundstage than either the D50s or the X8.
Returning to the Aune X8, it's a wonderful looking unit, with a great tactile and well-geared volume knob and a handy simultaneous line out. Sound quality is fine and would be fine in many systems. In Amir's testing the X8 would do well – there's no particular technical flaw and it approaches the D50s, with just a little less thwack in the bass. If the X8 sounded richer with less grain on the vocals it would be the most wonderful DAC/pre-amp on the market. It should be noted that the X8, unlike many pre-amplifiers, maximum output is the same as a DAC used as pre-amp: 2v, i.e. normal line-out signal. There's no additional amplification in the pre-amp or head room at the top, which can be an issue when powering amps expecting a stronger line in signal. I often had the volume knob at up to 3 o'clock while with most of my pre-amps I listen at 9 o'clock. The slower calibration on the volume knob is great but strangely there's no headroom on top for peaks, which at louder volumes becomes audible as a thinner sound in comparison to most dedicated pre-amps.
While the form factor with volume knob were exactly what I needed, I very reluctantly decided I couldn't accept less appealing sound in an "upgrade" and parted with my Aune X8.