I agree, that room is huge. The bigger the subwoofer you can afford, the better. Cheap subs aren't going to cut it in a 6500 cubic foot room! To maximize impact, I'd recommend nearfield placement of whatever subwoofer(s) you end up with. I'd check out the Epik Knight and SVS PB12-NSD as well - they might work well for you too (The Knight and A5-350 w/550W amp are my first choices for a room that size, though, considering your budget).