Dedicated Home Theater upgrade thoughts?[b][/b]

Current list of equipment...
m80's/vp150/qs8's/pb2 plus
in a (5.1 setup)
Yamaha rxv4800.....needs replacing
Panasonic AE8000U pj
120in. screen ...upgrade to AT screen so I can place front speakers behind screen(major waf).Room is 17'x15' with two rows of seats.

first question, what AVR should I be looking at to replace my failing (low audible buzz from all speakers)Yammy? I was looking at the Marantz 7007? Should I upgrade to 7.1 with two more qs8's behind seats or is that just a waste of money? Current sound is good but I want that wow factor. Any other tips or advice is much appreciated.