Why does my system now have shrill top end.

Fascinating how the circuit focused group analyzes the problem as an amplifier issue and dismisses all other possibilities pretty much out of hand, and rather forcefully. A microcosm of how audiophiles tend to think?

Kosst, thanks for the clarification about the multimeter measurements.

I also want to thank Jwpstayman for his very informative post about the OCOS cables. For one thing, it further reinforces suspicion that they have ultra-high capacitance. (I believe that when he referred to a "nobel network" he probably meant to say "Zobel network," which is something that is commonly used with ultra-high capacitance cables such as Goertz to minimize the capacitive nature of the cables as seen by the amp, that might otherwise cause ringing, oscillations, or even damage).

So based on his post a question for the OP would be if his OCOS cables have a "red" termination network, a "black" termination network, or neither.

Regards,
-- Al

Excessive DC on the amplifiers output can easily be checked even without a multi meter, just turn on amplifier while observing the woofer cone if it moves out and does not return to neutral position after the initial turn on bump - the amplifier have excessive DC on the output. It of course can move in also in case the DC voltage is negative.

Opening up the amplifier and checking rail voltages and Bias current is on a whole other level, and best left to someone whom knows what they are doing.

My gut reaction to this is the very long, highly capacitive speaker wires are at least contributing to this.  As someone stated above - try lamp cord.  

Best of Luck
Peter