What I've heard is that the problem has to do with Pulseaudio doing a sample conversion to 48Khz and some software equalizing to make the audio sound better and as worst, automatic limiting to create the so called "wall mix" effect to get higher volume output but killing the dynamics of the track as a side effect (I read that it's a protection so you won't drive too loud volume on the speakers to make them overdrive/break). As much as a normal consumer wouldn't mind these things, they add unnecessary overhead to the N900 cpu and distort the sound in a way that makes me quite annoyed.