I've made some utility programs for breaking up 6 channel
wave files into stereo and mono wave files, and going the
other way -- assembling 6 channel waves from stereo and
mono wave files. There's also a wave file player that
works better than aplay for playing 6 channel waves using
Alsa. The programs are based on libsndfile and are in
ftp://ling.lll.hawaii.edu/pub/greg/surround-utils-0.0.2.tar.gz
Also there are hacked files for ac3dec which add the option
of saving decoded ac3 as a wave file.
Greg