I have four Def tech power towers (2002x2, 2006x2), BP2Xs for rears, and a 2002 center. I am a newbie, but after reading multiple submissions, it appears that I will purchase a sub for HT. Which sub? My room is relatively large. With the return of some loaned money, price is not too much of a consideration (to a degree of course). I realize there are as many opinions as listeners, but are there some obvious moderate to high-end choices I should or should not consider? Also, would most people then suggest running the def techs as small and lowering the crossover a bit, or running as large and raising the crossover a bit for HT, with large setting and no sub for music? My receiver is a B&K 307AVR. Thank you.