What applications did you used ?
xmms have 6ch output plugins ?
I don't use xmms so I don't know.
Now I'm using Xine
It uses an open source library for the AC3 decoding (liba52
), and I believe that MPlayer uses that one too.
Maybe you'll need to install that library and some xmms plugin (if there's any) in order to get 6ch support. If not... try Xine
You won't be dissapointed.