I have found that the sound quality from all of the Sandisk unit's my wife and I have owned, has been really good. They are also devoid of distortion too (I'm guessing that there is an internal gain govenor like that found in higher-end HT receivers). I thought that the old E130 I had, combined with it's original headphones sounded quite good, and I ended up using the 130's IEP's with my Fuze, as they sounded better than the ones that came with the Fuze. My wife borrowed and accidentally broke my 130's IEP's, so I bought her some JVC HA-F67's for her Fuze, and that combination was really surprising. Since I laundered my Fuze, and replaced it with a Fuze+, I got some of the Xtreme Xplosives IEP's, and they are STUPID loud on my new machine.
The SQ on these machines is superior to other mp3 players I've tried, and I found that with the right headphones, its as good, or better than the offerings from Apple.