I have two front speakers, two rears, a center and a sub. The front speakers have two sets of inputs. I'm looking at buying the Onkyo TX-SR606 as the receiver but want to make sure everything is going to work right. On the back of the receiver there is a set of "surr speakers" and "surr back speakers" that says something about front also... Why are there two sets of rear outputs? I read this from the amazon description, I guess thats what I need but just want some clarification. So why is it called Surround Back?