Hi All, I am new to this so here goes.... My current set-up is 5.1 and: Receiver: Yamaha HTR 5560 Speakers: Polk Audio RM6200 Speaker Wire: Monster Cable I am thinking of upgrading to a Yamaha RX-Z7 or RX-V3900 Receiver. My question is, can I / should I keep the Polk Audio rear speakers. And even if I can, what are some suggestions for good speakers to place on the rear for this set-up? I was also thinking of keeping some of the Polk Audio Speakers for a 7.1 Surround sound and adding new rear speakers. Any advice would be greatly appreciated.