OK, I encodeed a 2 disk movie with the original 5.1 ac3 soundtrack and a VBR stereo mp3 commentary track, all is well except that when I switch to the commentary (using zplayer) the sound is distored BADLY, it sounds like a badly tuned radio, I can hear the voices, but it sounds like the gain has turned up so high it's causing distortion.

The mp3 that was muxed (and re-muxed) into the .avi plays standalone fine, but when muxed in sounds like shit

Any ideas anyone??

I once had problem with such avi with morgan switch, maybe that would help:
before switching to mp3 track I had to change speakers config in AC3 filter (that one from WinDVD) to 2 speakers, if I didn't funny thing happend

and what do you use for muxing? maybe Avi Mux GUI would help you

I use virtualdubmod for muxing, I'm wondering then if it's a switching problem. Thanks for the hint, I'll take a look later

Not a switching problem, it turned out to be something with the muxing process, using AviMax GUI fixed it, thanks for the help Carlos66