i'd suggest an outboard electronic x-over - the marchand xm-9, & a pair of vmps subs, which model depends more on room-size than anyting else. this set-up, w/a decent used solid-state amp, will cost less than even *one* comparable powered sub, even if ya get a pair of vmps' biggest model. and, ewe *won't* find better specs than that of the vmps larger sub at *any* price. also much more flexible, as the marchand xm-9 allows a multitude of settings, & more transparent electronics, too, imho. also, having two subs allows easier room set-up to optimise soundstaging/room interaction, & allows for much less distortion for any given output level as well.
doug s.