I have some info that may be useful to someone experiencing the distortion on audio mixdown issue.
I was experiencing a similar thing yesterday. When I exported an audio mixdown from Cubase I heard the bitcrusher type distortion when I played the exported wav file on Winamp or VLC Player.
However if I re imported the same mixdown wav back into Cubase it played fine with no distortion.
I managed to eliminate the distortion problem by ticking the box Release Driver when Application is in Background on Cubase audio settings.
(It appears that (in my case) it was a monitoring issue, and that distortion was not actually being included in the mixdown).
Add on: I think this is an issue with my particular soundcard (Komplete Audio 6). I have also noticed another workaround for this - when playing back the exported mix if I change the sample rate on the soundcard interface from 44.1k to 48k this eliminates the distortion.