Mounting a center on the ceiling will take a big toll on the overall sound. It will screw up the imaging so bad that it's not even worth having a center in that situation, especially since this is primarily for music. Your polk sub is pretty so-so, I would sell it and get something better. Check out Hsu Research, Outlaw Audio, Rythmik, and SVS for good affordable subs. Make sure you don't spend a lot on the surround speakers, they are not going to help music much, in fact I would just ditch them as well, or leave the ones you have. For sound quality, your money will go so much further if you focus on a 2.1 system.