Maril- I was curious about the solution to the comment Jea had made up thread. There, Jea said:
"JMHO, if the subpanel will be somewhat close to the audio equipment’s branch circuit wall receptacles (15ft or less) imo, that kind of defeats the purpose of multiple dedicated branch circuits for the purpose of decoupling the power supplies of audio equipment from one another. Especially Digital from analog.
Imo, the amount decoupling is largely due the length of the branch circuit wiring impedance of the branch circuit wiring used, especially NM-B cable (Romex is a trade name of NM-B), or MC cable. (Both use THHN insulated copper conductors.)"
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I don't know the answer, in fact, I had never realized that was an issue, so that's what prompted my question.