There's a similar thread over on AVS right now, general consensus is for one sub, the Epik Sentinal is the way to go for the dollar, although the graph doesn't look to be all that, real world performance could differ obviously. The PB12+ is pretty sweet too. I still think you'd be way better off with duals in a room so big.
I have spoken with SVS and HSU customer service/tech support pretty extensively in the last week, and they are both exceptional.
http://www.avsforum.com/avs-vb/showthread.php?t=1199217
