Well, I don't really use the music player since I got a Sansa Fuze.

But the output sound quality of N900 is good imho compared to N97 and Nokia 5800xm since I own them both.

N900 is slightly better than 5800xm in terms of clarity.

Another thing is, I would like to say why the scrolling of the playlist in N900 media player is not as smooth as 5800xm or N97? Thats weird since the hardware is better in N900. I guess it is the firmware.