I have a Yamaha 5560 6.1 Receiver. I dont know all that much about the upper eschelon of HT. If I hook up an Amp to my system what kind of difference will it make. If its a drastic one, what kind of Amp should I consider in the sub $400 price range (less expensive the better.)? Is there something I can hook up to my Receiver to give me 7.1 audio? A lot of questions, I know, but I thank you for your help.