You will get 100 different recommendations for sure.....well, okay, maybe not 100.
So $6K for 7 speakers & 2 subs?
Personally I would just do 5.2 (for most rooms 20' x 18'), but 7.2 is cool too especially if you have a very large room.
Most of us own speakers & subs from 2 different manufacturers. For example, speakers from Salk, Ascend, Revel, KEF, B&W, NHT, Focal, etc, but subs from Funk, SVS, HSU, Rythmik, etc.
Most of us also own separate ext amps, but I think your AVR will be fine.