All of that book theory is fine, but it does not reflect real world audiophile experience. Thousands of audio enthusiasts run their systems on multiple dedicated lines -- on the same 120V leg -- with no ground loop issues. What is the person with the large audio or HT system of multiple high powered amps supposed to do ? Run everything on a single 20A circuit for fear of having a ground loop ?
I didn't say multiple dedicated lines would necessarily create a ground loop (many manufacturers isolate the signal reference ground from the chassis which is tied to the AC safety ground).
Only that they would acerbate any ground loop issues that do exist.
Your post implied that as long as they're all tied to the same 120 volt line, this would prevent ground loop issues, which simply isn't the case.