Performing a comparison between the
ifi Zen DAC and the
SMSL M500 is pretty easy: just look at the two reviews that Amir did. I currently do not plan to do any sort of side-by-side comparison between the two. Mostly because I don't have the time, but also because the ifi Zen DAC is way out of its league compared to any of the DAC/amp combos in this review. SINAD is really low, linearity is mediocre, IMD is poor, and power is anemic. The three DAC/amps in this comparison are all near-SOTA devices.
If you're looking for subjective opinions on the sound quality that's not what my comparisons are about; they are measurement comparisons. I'd suggest opening a new thread if you want subjective sound quality comparisons.