Since it is the consensus that speakers make the biggest difference in a system, and that the center channel gets 80% of the movies' audio soundtracks, it is easy to conclude that the center channel would have the biggest impact.
What next?
Excluding the front speakers(Monitor Audio PL500) what has the most impact on surround sound? The center, rears, or AV receiver. My center is a Monitor Audio Gold C350 and I'm thinking about going to the Monitor Audio PLC350, but won't have an opportunity to hear it. My rears are Monitor Audio Bronze and I could go to Monitor Audio Silver speakers. I have a Marantz SR5011 AV Receiver and could go to a better AV Receiver. What is my best option?