Looking at Yamaha RX-V765BL 665 Watt 7-Channel Home Theater Receiver, since it is not 7.1 I cannot use a sub, correct? Although the back of the receiver has two ports for subwoofers as a pre out. What is that?
http://seattlecontent.s3.amazonaws.com/YAMH9/09/08/RX-V665/rxv665bl_back_large.jpg