Why does my system now have shrill top end.

SPEAKERS ! After trying another amp and/or cables I'd try another set of speakers that a friend can bring over. The tweets may've gotten damaged somehow - if that's the case there's nothing you can do to get sweet music back. Find out.

like @jea48  I am waiting to hear if taking the P5 out of the system helped, although his description of the problem didn't seem like noise to me.
Haven't heard from the OP in 5 days....

OP last commented saying he was going to swap the amp this weekend and if not that then look at ac.
This weekend could well be late tonight, we do not know his work schedule.
However if not the amp, I certainly hope he does not jump straight to ac possibilities without at least swapping speaker cables no matter how unlikely that scenario may be. Its cheap, quick and easy.
I am thinking the amp swap will reveal plenty but we just have to wait for now.

Thank you
Kevin

Thanks for all the great suggestions. I turned off all lights in the house and it made no change. For the HOI I changed the power cord from a PS Audio AC5 to the stock cord that came with the amp and although it had no effect on the upper registers it seemed to focus the sound stage more. I guess this is left for another discussion.

I wanted to switch amps but the 5 channel unit I use for the surround sound room is much too heavy for me to easily move. Hopefully I can get a friend to help me and will report back afterwards. I too think it must be the amp but this test will tell for sure.