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You can extract the audio stream from the avi file using Nanub
then edit the audio file using GoldWave (It is pretty capable wave editor)
and split stereo track into two mono tracks then recompress each of them
using LAME and VBR Mp3 (Quality will not downgrade this way) but you
will have to tinker with options a bit to get 2 files similar in size to original
audio file then you can:

1. Save only video part of the movie (NanDub) and include this 2 Mp3s
when you burn the CD (you can make ini file that will give you otion
to select wich audio you want to play in BSplayer)

2. Remux that video part only (NanDub) with 2 separate audio streams
in it you can then switch or select which you want in BSplayer (I am
pretty sure that NanDub can mix 2 audio tracks into 1 avi)

In my opinion the second solution is better.