I have the 990/7125 in a room that is half the cubic footage of yours (16x14x7.75) and it does so well at modest volumes that I bet that it would be fine for your bigger space.

You could go with the 7700 and its 200 WPC, but I'd put the extra money elsewhere (DVD, HD-DVD, display, etc).

Bears, beets, Battlestar Galactica.