Yes to everything. The distortions are heard pretty much on anything that has heavy base regardless of the source - youtube, flac, mp3. The distortions are present on PC, Mac and phone.
I question the quality of the amp in this thing. Such a tiny unit pushing more juice than GSX1000 and ZxR - there's gotta be a trade off.
The Amp seems to handle Bass differently than the Sennheiser GSX-1000.
Go to the sound test in volume properties on the GSX-1000 and test the "Subwoofer".
Notice how it sounds? It sounds like a drum, right?
(My X-fi Fatal1ty also has the "drum" sound on the bass test, but see below).
Now go to the X-fi and test it.
It sounds like an actual subwoofer rather than a 'drum'.
I noticed that on my old X-Fi Fatal1ty PCIE:
If I set the creative console panel to "Headphones" (so it uses CMSS 3D, their older HRTF for 5.1 surround sound), the bass sound also sounds like a drum.
But when I set the creative console panel to "5.1 surround sound", it sounds like an actual subwoofer..
I'm guessing there is a lot of gain in the bass. Probably from it emulating an actual reference loudspeaker room with an actual subwoofer, and many headphones are not designed for a bass gain like that. My V-moda Crossfade 2 handles it quite well (tested up to 50% volume in something massively bass heavy---The Diablo 1 "Cathedral" map music...Probably try a different headphone preset and mess with the EQ.