The Ultra 12's (especially duals) will work much better than a supercube. There's no real substitute for size. The supercubes are more aimed toward very small rooms where space is at a premium. They do what they are designed to do very well, but they just can't put out enough to fill a larger room.
Television: Mitsubishi WD65737 DLP
Processor: Emotiva UMC-200
Amps: Carver AV 806x/Behringer EP4000
Mains: DCM TimeFrame 600 Center: AT 453C
Surrounds: AT 251.1 Sub: Danley DTS-10
Blu Ray: Panasonic DMP-BD655