New to HT, just acquired a Yamaha RX-V630. This unit can run a 6th speaker channel, rear center. I'm not using it at this time; in the room I am using, placing a rear center would be difficult although not impossible, and I am wondering if it is worth the hassle. So, what is a rear center good for? Where do you place it - should it be inline with the surrounds and directly between them, or should it be placed further behind the listening position?