I don't have a 600, but have a 505 and imagine the mp3 player would have about the same functionality (I could be wrong though.).
Like quillaja, I wouldn't recommend the readers for use as mp3 players. Using the mp3 player will drain the battery quickly and it's easy to leave the player on after you are through listening, which will cause the battery to drain.
I recommend buying a dedicated mp3 player for listening to music. You'll have much better luck than trying to use the reader!
dordale