I own and love Boston speakers but I am not that big on their subs. They are OK, but I have heard much better. You might look at Paradigm, HSU, SVS, REL, and Velodyne to name a few. I have yet to hear the SVS but they get great reviews. I have listened to a few models from all the others I mentioned and they all seem to be better subs than Boston, model for model. Of course this is just my opinion.
Shinerman.