Just a bit of an update. I hooked everything up *outside* of the cabinet. Components in a stack, IR pickup sitting on top. Everything seems to operate normally when both the "remote" pickup and the built-in pickups are enabled and receiving IR commands.

That being the case, I'm going to try it without any kind of interrupt switch and see what happens. I can always go back and change it later--but this way there is one less thing that can fail.