My sense guys, based on auditioning PC's on all my gear over time, is that the best bang for the buck is to try in the following order:
1) Source component(s).
2) Preamp.
3) Amplifier.
4) For ML's, the speaker.
Seems to track with what component(s) is / are most sensitive (read most audible) to justify trying after market PC's within the context of it's contribution to the total / aggregate sound of your system.
I'm not saying that the amp / PC interface is insignificant but that you will be able to hear its audible impact more clearly after you have replaced the stock PC cords in your source / preamp components.
I use the Cardas Gold Reference ($500 / ea.) for my amplifier and PLC, which plug into a dedicated 20 amp AC outlet, Shunyata Venom ($99 / each) for my Summits, which are also plugged into another dedicated AC outlet, and Mapleshade PC's ($300 / ea.) for my CDP and preamp.
Rich has previously posted about the positive impact of the Signal Cable PC's he installed on his Summits and I have no doubt regarding his observations.
The main variable is how transparent your system is, which will effectively dictate how audible a PC will be.
My gut, when all is said and done, is that each individual system will respond differently to after market PC's. All that matters is that the individual hears a positive musical difference that justifies the product cost.
GG