I would look at the Rel subs. I looked at a lot of subs and the Rel out did them all.
Subwoofer w/ most SPL's For Music Only System
Considering a subwoofer for a music only system. Looking for a sub that will be musical and yet have plenty of headroom to play it loud or turn it down. In other words, powerful bass with the ability to go into the higher spl's if turned up; the kind of sub that has the capability to play a high volume of bass without the benefit of connection to an LFE channel. Considering the Sunfire Signature, Velodyne HGS 15, Earthquake Supernova 15.