Try driving ONE speaker on one channel. Then, try that same speaker on the OTHER channel. Then, do the same sequence for the other speaker.

It might not tell you anything. But it might tell you something.

There might be something wrong in one channel, or in one speaker.

Hook the Polks back up. You might have fried something in the amp when you transitioned from one set of speakers to the other.

I'm VERY surprised that amp is having a problem with the M80's.

bibere usque ad hilaritatem