Gents,
I have never heard this discussed, so thought I would present it here.
A couple of things to try that may help improve the sound.
First, can you plug your entire system directly into the wall socket? IF not, ok.
Second, do you have some spray cleaner, leaves no residue? If so, follow these steps (even if you use an AC line product, such as an AC conditioner). Make sure you do not plug in both ends of the cord at the same time as if there is any arcing, fire could result.
a. Remove Both ends of your power cords from AC outlet and all components. This is to prevent any arcing.
b. Spray clean one end of a power cord and plug and unplug a couple of times. Then spray the same end again and plug and unplug a couple of more times. Leave unplugged.
c. Now do this to the other end of the same power cord. Same procedure, and let cord dry.
d. Now do this to All your other power cords, including any AC conditioner or other AC device. Let cords dry.
e. Plug in your power cords to components.
I just did it and it to my monoblock amps and it made a musical difference. (My preamplifier did not as it has 6 stages of heavy filtering.) Hope this helps yours also. Worth a try though.
Cheers
steve