I have just recently bought Mission 705's, which are full range towers. They each have amps which power 4 8" woofers. Because of this, I have no need for my 12" subwoofer. In fact, when I turn the sub with the towers, the bass is weaker, and I suspect that they cancel each other out. Is there a way in which I can still use my sub by tweaking crossover freq., phase, or maybe using them for my rear surrounds? I'm not sure whether to sell it or use it.