The real thing you want to do here is isolate the problem and see what you can hear and what might be causing this... The quoted specs are "Good Enough" and it's doubtfull you could tell the difference with any better numbers, from what I remember -- especially considering you're playing lossily encoded mp3s.

The way to do this is to do what was sugested orginally, and check a wav file to see if you hear the same problems with the output. Get a wave file by using Exact Audio Copy and ripping it from a real (non burned) CD. If the wave file corrects the problem, your problems lie in music match jukebox. If it doesn't, your problem lies in the empeg output chain. It's very possible that your equalizer is set to flat, when you want some sort of boost in the curve.

If the wav file sounded good, but your mp3's don't, you need to change encoders or encoder settings. The majority of people now recomend Lame with the -alt-preset-standard VRB setting. Both EAC and LAME are free, so that shouldn't stop you...

Good luck chasing the perfect sounding system, it's a very expensive game :-)

Matthew