Few ideas..
Hey Vern;
I ran into a problem similar to yours some time ago. When I was initially wiring one of my systems, I used some small gauge wiring (18 or smaller) when I was checking to see where I'd be able to mount my surrounds. Well, I forgot to swap it out w/the good stuff after I'd set everything up and sure enough, whenever I got down to a certain level (can't remember what level due to severe case of CRS... ), the protection mode would kick in.
Took me a little bit to figure it out, but sure enough, it was the cheap test wire I ran to my surrounds. Once I swapped this out, I was good to go all the way down to +05 on my Denon AVR-3803 (reached receiver limit). If you think it might be related and you have some extra 16 gauge or lower speaker cable, may want cut some new runs to each speaker and test. While this may sound a little rudimentary, this is one of the easiest things to check and is often a cause for receivers kicking into the protection mode, assuming the receiver isn't problematic. If you don't have at least 14 AWG wire running to your surrounds, you may want to consider this. Sometimes there is far too little consideration in using decent, heavy gauge speaker wire. Once heavy wattage is pushed to all channels, the gauge can become a factor.
While your Onkyo may not have exhibited this behavior, did it push as much power to the speakers as well? If not, you may not be comparing apples to apples. Are you running a sub with this setup or is it just the 602s? If you're not and you're running the 602s as large, they may not have been able to handle the low end power surge during one of the dynamic passages which may have triggered the protection mode on the receiver.
With that receiver and those speakers properly wired and calibrated in that size room, you should be able to pump out reference level dB over a decent period well before it goes into protection mode. -TD
