Today, I recconected the front and center channels directly to the Onkyo. When I cranked the volume to 82 (THX Ref) level, the Onkyo shut down, and restarted. It went into diagnostic mode, and reported a "check Sp Wire" error. I restarted it and all was good. Since this is now also a problem with the AVR itself, are there any ideas as to why this happened? I'm thinking either my AVR got too hot, but that's just a guess. Any help is much appreciated.
You seem to me someone who lacks perspective on what speakers like yours are capable of.
Now what any manufacture says about power handling ability is just a wild guess. Generally a speaker will be damaged long before the power level quoted by the manufacturer is reached. The reason is that music is complex, and can put a lot of power in any given frequency band at any time.
If I have this correctly the EMO shuts down at high power, and now the Onkyo shuts down when previously it did not.
My strong hunch is that you have already damaged your speakers.
I suspect one or more drivers have had their voice coils overheated, so that the insulation on the wire coils has started to break down, and you now have some shorted turns, and the impedance has dropped. The most likely drivers to have suffered this are the midrange drivers. There is only one in each speaker and they cross at 340 Hz and 2,700 Hz, so those drivers are taking an awful lot of power, especially on a lot of program. Very high powered midrange drivers are very rare indeed and you will not find them is speakers in that price range.
Generally if you are designing a speakers for high power with crossover that low, then you always use two midrange drivers in MTM configuration. That is what I do.
So you need to remove all the woofers and the mids to measure their DC resistance. You will need to get the spec. from Polk. Any drivers with a DC resistance below spec. will need be reconed or replaced. If you don't then you are going to ruin your receiver or amps.
You need to have more respect for your equipment and operate it in a less cavalier manner.