The Polk SW505 is the only Polk sub I would recommend. But the store he is purchasing his equipment at doesn't carry them. To the OP. Can you purchase a sub through the internet?
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