Yes, all is finally right with the system. After extended checking and rechecking with the electrician about the home's electric system, I then did a component by component process of elimination -- saving the amp for last because of size/weight, its no picnic to handle and ship. Of course it turned out that the amplifier was the issue. I don't know the technical details, but something got overcooked in the amp, and the cause was not determined -- perhaps due to electrical surge/lightning strike nearby. I (unwisely) did not have surge protection in the system at the time.
Anyway, the good people at Audio Classics identified the problem and fixed it. BTW, I can now report happily that installation of the dedicated line (first thought to be the problem) has yielded huge sonic benefits; the system is now sounding better than ever, far better.
Thanks for all the helpful responsive comments.