I've patched up Timidity++ to play in 4/6 channel surround
using the Alsa driver on Linux (or perhaps other systems
with Alsa). Source files to replace those of the current
CVS version of Timidity++ are in
ftp://ling.lll.hawaii.edu/pub/greg/Timidity51.tgz
The included Alsa output driver will also handle 2-channel
24 bit output. Probably only works with a recent version
of Alsa.
Greg