Why does my system now have shrill top end.

I too think it must be the amp but this test will tell for sure.

Hopefully Kosst will take my response to this in the constructive spirit in which it is offered: If the problem goes away when the amp is changed, while it would substantially increase the likelihood that the Pass amp is the culprit, it would not by any means be a conclusive indication. It could simply be that the other amp is less sensitive to the effects of a speaker cable having very high capacitance.

Also, can you answer a couple of questions I had raised earlier:

1)What is the full model name of the Ortofon Black cartridge?

2)Do the OCOS cables have a "red" termination network, a "black" termination network, or neither.

Good luck. Regards,
-- Al

About a year ago I was experiencing system symptoms virtually identical to those the OP has described. At some point after much thought, frustration and experimentation, I replaced my speaker cables and the harshness disappeared. 

30 feet of Monster Cable or 12 gauge TW cable from the hardware store will be an easy and inexpensive experiment. Hope this helps.

I'm sure someone has already discussed this possibility, but on two different occasions when your problem arose in my system it was as big a mystery to me as it is to you. I was able to eliminate the problem by addressing the dressing issue and insuring that IC's and PC's were not running parallel nor were they passing close to transformers. Since I did a tear down and reassembly I'm not sure where the villainous wire(s) were but the problem did arise after I had been fiddling in the back of the equipment reconnecting/relocating equipment. FWIW.