Big room at movie theater volume. If you don't have big power you need something efficient like the Klipsch mentioned. Though for many Klipsch have a love or hate sound.
A good option IMO is the current deal on the Def Tech 8060STs. $2000 for the pair which includes a 8040 center and a pair of 8040 surrounds.
Klipsch RF-62II, RC-500, RS-400, SVS PC12+,
Def Tech SC8000
Harman Kardon AVR 1600
PS3, Apple TV, Sharp 70" Qattron