What commerical audio system tweaks provide sound quality improvement??

Geoff, you would have to be cleaning ONE outlet, the hot one, with a material that becomes conductive, for one reason or another; e.g. wet with perspiration. That and a path to ground, no matter how elusive or invisible.

And Geoff, I did not insult you nor your intelligence, so pray do not insult mine. There is no need for that.

Now you're being ridiculous. And argumentative.

Yeah. Right.

The $15 Ikea butcher-block cutting board under floor standing speakers.