9.2 vs 7.1
I have a 9.1 setup with a single 15 in sub and really like it. Only 7 speakers play at any one time, but with blue ray movie having Front Height and surround back speakers make the system very dynamic depending on the format of the movie. Having helicopters moving in the front height channel or things coming from behind you with the surround back is a nice effect. I can't imagine going back to 7.1. Music is also great in extend stereo, DDPLIIz, DDPLIIx, or just 2 channel stereo. Using front height speaker is like adding an addition to your mains. I thought about a second sub, but have more than enough bass already. Just my .02 on the topic.