@kennyc Thanks for your list. Because I have an Audience conditioner in the wall protecting my gear -- and it plugs in directly -- I have not yet been able to do an experiment with power cables at the wall. In my new room (which is done but I have not moved in there yet) I will try it. I will also try @audphile1 suggestion to plug in directly to my dedicated outlets.
I spent most of my time and money on the interconnects so far. That was largely because I did not really have good ones and I needed to get some. Also, I don't know how bad (or good) my power is, so I figured I would try improving the signal path first.