(Regarding an A/B connection to the amplifiers) He talked me out of it very quickly, with the same arguments that Smoker_Man stated -- there would almost certainly be a lot of noise introduced into the system.

Not if the switch is done right. I've wired guitar pedalboards in this fashion, routing signals every which-way. If it's done right, it can be done noiselessly. Admittedly, car audio is a different animal, but...

Didn't someone, a long time ago, post something to this BBS about an off-the-shelf box which did precisely this? And if memory serves, it was even a Sony product and it did the job automatically (although I don't remember whether it used signal from the audio or the remote turn-on lead to do the switching). They even posted a picture of it.

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Tony Fabris