Rightmark didn't find any problems with the device. In 2V mode (red & blue light together), 80dB S/N ratio & dynamic range with USB power. 90dB without USB power. 70dB separation as a line output without USB power, which is consistent with other good quality near-zero-ohm headphone jacks. No issues with distortion at the Emu 0204's 2.17V output at 100 volume in Windows in 2V mode. Sounds nice.
Not quite as much gusto and bite in the mids and highs as the E7, but bass is more tuneful and lacking in the E7's wooly quality into higher impedances. E6 is slightly more refined and grain & grit free in the midrange. Having the USB powering the E6 seems to give some (but not all) of that gusto and control back to the E6, at the expense of refinement and noise floor. This is obviously even more apparent when the battery is running low, which there doesn't seem to be any visual indication of.
With low impedance headphones like the KRK 6400, the E6 is superior. With higher impedance headphones like the ER4S, there's no question the E6 is an improvement. I assume the smaller battery will become a bigger problem for very high ohm cans. Mostly good in my opinion compared to the E7 except in the 50-70ohm range, where the E7 seems to have the right combo of current and voltage even if it's not as refined. With headphones in between like the Fostex T50rp or my modded Sennheiser HD25, it's a toss up. It changes them some good, some bad.
T50rp sounds more constrained and less resolved on the E6. HD25 is rather midrange-oriented with the E6 while it sounds downright dark and bass heavy on the E7, while retaining a bite up top. I definitely prefer the KRK on the E6. Tron Legacy's score blows me away with that combo. Ditto with the ER4S but with a very different sound where orchestral recordings are more ambient, warmer, more real.
Synthetic or produced music sounds more artificial with the seams and artificial distortion and other processing more apparent. I'm not too fond of how the E7 drives the Ety. It's both warmer, but dryer than the E6 with them. Maybe that's more accurate? I don't know. I can send the 0204 headphone jack (prior to clipping) at 3 o'clock into the E7 at 60 (max volume) with the ER4S and get symphony hall volumes (try Recognizer), but it doesn't sound as liquid or engaging as the E6 at lower volumes. I don't need to crank this little guy to engage on the Ety. Perhaps that "dryness" is actually the E7 just fleshing out more low-level detail while the E6 is glossing over it? Don't know. And the E6 sounds fine with line outs while I find the E7 does better with headphone outs going into it.
Neither the E7 or E6 are clean with USB power when maxed out. Buzz. I do find I also hear quite deep into the sound with the E7 and modded HD25 combo, though: the difference between MP3 encodings compared to their lossless versions is night and day.
