I'm moving into a home with a Linear hardwired intercom system with a total of 8 stations and various in-ceiling speakers. I'd like to use the stations to play sound from a receiver. Using a Linear DMC-10AWP device, I can input sound to the Linear system via RCA cables. However, in order to mute the sound when the intercom is used, I need a box or other piece of hardware that will mute or redirect the sound upon contact closure from the DMC-10AWP (the 3.5mm mute output).
I was thinking that an A/B switch for RCA cables would work; when the contact is open, "A" or my audio source is selected, and when the contact closes, "B" or nothing (disconnected) is selected. However, I can't find one that works on a dry contact closure. Any other ideas? Is there a straight-through "mute box" out there I don't know about? There is no mute input on my Onkyo AVR.