My home theater/rec room is pushing 8,000 cf and my Denon 2805 has no problems. Most Denons will have no problems with any of the axiom lineup. I would say buy something that is within your budget and that has the features you want. THX is ok, but don't just buy a receiver because it has THX designation. Most decent AVR's would be capable of carrying the THX designations, if the mfg decided to pay THX for the certification.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85