I missed that... you are getting overheating faults? That is definitely a bad sign.
As mentioned above, the Polk Speakers are not friendly electrical loads. You could be well on the way to blowing out your AVR.
Do you employ an active cooling solution on your AVR? Something like the AC Infinity Aircom units:
Your source to create smart growing systems with components including advance grow tents, inline fans, clip-on fans, LED grow lights, and UIS™ controllers.
www.acinfinity.com
Or more simply just some 120mm fans:
Your source to create smart growing systems with components including advance grow tents, inline fans, clip-on fans, LED grow lights, and UIS™ controllers.
www.acinfinity.com
Your source to create smart growing systems with components including advance grow tents, inline fans, clip-on fans, LED grow lights, and UIS™ controllers.
www.acinfinity.com
(Just examples, but I use an Aircom similar to the first link and it is great!)
Anyway, the other aspect of this is that you may well be overdriving the AVR with multiple Polk Speakers. Getting good amplification that can handle the current loads posed by those speakers is important. Bi-Amping will not help that, though, just to be clear.
The electrical load of those speakers will generate a significant amount of heat in the Amp Stage which then must be dissipated. Heat is the number one killer of electronics.