I recently picked up a Pioneer VSX-S520D 5.1 receiver that has an amp to drive a sub-woofer as well as a pre-out. I have a Klipsch Quientet V set of speakers for front, center and surround but need a sub-woofer to complete the setup. I prefer to drive it with the receiver itself so I am looking for a recommendation for a passive sub-woofer with a 10" driver. The specs state that the amp puts out 80W RMS into 4 ohms (much less if it is 8 ohms) so there really is not a lot of power to drive it. Any recommendations will be appreciated. Thanks in advance.