If it is a dedicated HT I'm assuming primarily movies. My room is 13x18x8(WxLxH) and run an Outlaw 1050(65Wx6) driving my 170's L/R, B&W center and Onix Rocket UFW-10. For music and movies the 170's are great. For music the 10" sub is great. For movies it does a good job, but if you can get a good 12" sub go for it. It will give you more of that "air shaking" ability that will benefit movie soundtracks. More than anything else, a good sub can make or break an otherwise good system.
Ed
* Sierra-2EX's W/V2 crossover upgrade
* (2) Rythmik F12's
* Parasound Halo P6
* Audio by Van Alstine DVA-M225 Monoblock Amps
* MiniDSP 2x4HD For Sub calibration
*World's Best Cables Canare 4S11 speaker cables