Honestly, when dealing with MP3s, the sound "quality" is mostly determined by two things: The encoding of the MP3 itself, and the headphones that you're using.
I haven't even tried using my 600 for MP3s (since I have an iPhone), but the play options are probably pretty minimal. However, if you don't care about fancy features and just want it to sound good, you'll probably be fine as long as you get decent headphones. Might I recommend some high-end noise isolating (NOT cancelling, that's unnecessary) earbuds from Shure?