Nonoise, if you happen to have a multimeter can you indicate what your line voltage is, at the time of day at which you most often listen?
Also, my compliments on voicing the thought that LESSENED ability of a system/room/power source combination to reveal the sonic effects that may result from a tweak can be due to BETTER quality of the system/room/power source. That is all too often under-recognized IMO, while the inverse possibility is often cited by "believers."
As I have said in a number of past threads, countless technical reasons can be cited why a given system may be able to resolve differences between tweaks or components that have nothing to do with the ability of the system to resolve musical information. Or that may even be inversely correlated with the ability of the system to resolve musical information.
Best regards,
-- Al