Well, I just tested Spider-Man (movie-only, one audio channel, no subs, constant bitrate):
With AC3 6ch: 4.30GB (4,626,225,152 bytes)
With AC3 2ch: 4.08GB (4,389,842,944 bytes)
LOL, took a little extra time to get the correct 2ch. There's three of them, and it happened to be the last one. Somehow I doubt this is enough savings to have a dramatic improvement in picture quality. Maybe just a tad in longer movies. Maybe I will just stick with the 6ch stream. You guys are right...I'll be kicking myself later for it. Perhaps I'll invest in a quality 6ch speaker set in the near future. Oohhh...wireless...yeeeeahhhh...