Getting back to the OP in quantum products, heres my 2 cents worth. I started messing with tweaks back in the late 70s. My first tweak were the Discwasher Gold-ends which were interconnects with gold plated RCAs and a better wire. Egads! They improved the sound of my them system (Yamaha C810, Braun L710, Garrard t-t).
As years passed, I tried other tweaks and eventually had to opportunity to audition/review some PLCs in no specific order: (Exact Power SP/EP, Blue Circle Music Ring 600, Silver Circle balanced power supply, Audio Magic Eclipse II, RSA Haley and Duke, Earthcalm Scalar, Powervar isolation t-former, Quantum Symphony Pro).
Out of these, the clear winners were the Quantum Symphony Pro and the Powervar. Interestingly, nothing plugged into the Symphony Pro, it just went into the wall and turned on.
Dealing with the Quantum Pro- Ive posted this elsewhere, but my impressions were that it affected the atmosphere in the room. Shortly after plugging it in and with no music playing, my wife came into the room and commented how it felt different as in more relaxed. She didnt know what I had done and looked around as if I had cleaned or rearranged something. Mind you, she rarely comments on how my system sounds so this was epic. My impression was the same and Id opine these devices affect the person more than the electronics, but thats just a guess.
Ive quit trying to figure out the how and why these Quantum things do what they do and just learned to enjoy them.
Now, the price of these devices, especially the new Quantum Q4X, is a legit gripe, but 90+% of whats being sold is way overpriced like $10K speakers with a driver cost of $400.00 and dont ask about cabling.
Im looking forward to some Q2X/Q4X to show up on Agon. Ill be snatching one if the price is right.