I have a cheap Yamaha receiver hooked up to two monitor 60 Polk tower speakers and one cs2 center from Polk. I have two cheap Yamaha surrounds hooked up as surround speakers but they usually are not used. So I have a 3.0 system right now. Whenever I play music above -9.5 volume on the reciever it will shut down. When I turn it back on it says "check sp wires" and will run as normal until I turn it up too loud again. What is causing this? I just checked all my wires and they look fine, and there should be no reason for my reciever to crash only playing three speakers.. Any ideas?