If you can afford it, go for a pair of a 12" Hsu subs. They will offer much more extention. In this case, two is better than one. SVS also has good offerings. And of course there is always the DIY method. Last time I checked, Crutchfield was selling Infinity Kappa 12" subs for $180/pr shipped. Those drivers, coupled with proper amplification, a strong box, and a true stereo implementation would yield a powerful and accurate subwoofer setup.