@jrareform I have a voltage adjuster (occasionally line voltage drops down to 90V) and a power conditioner (both Furman). I have compared speaker cables (Cardas 101 AWG 14 vs. Pearlacoustics AWG 4-5: so MASSIVE DIFFERENCE), and I can't tell them apart. Put them on A-B speaker outs bare wire (no possible effect of connectors) hooked up simultaneously, so could switch with a click of a button. Absolutely nothing different.
I compared some interconnects, no difference: standard, some Cardass, BlueJeans.
Power cables: the problem is that most aftermarket cables are not UL/CE listed, so present a home insurance liability. And after all, I don't buy it to begin with.
My room is also treated, I get my soundstage etc. I do notice differences between tubes, phono cartridges, phono preamps, speakers, even a tiny bit with DACs, but a lot of audiophile stuff I tried and cannot replicate (e.g., digital delivery software: Roon vs. Audirvana: nothing; USB cables: nope). My system is listed here on audiogon if you care to check it out.