FIRST, check the current products or DIY build plans used by SO2R contest operators (e.g. DX Doubler at $225 USD).
What you propose is the "opposite" of how broadcast and audio/recording studio mixing consoles normally work.
In those cases, multiple "source" INPUTs (AP audio news feed; tape (cart & reel to reel); phonograph; compact disc/digital audio; MP3)
are mixed and then sent to a common OUTPUT (radio transmitter and/or Internet streaming audio/music server).
However, the solution that you desire is frequently used by commerical network "pooled" microphones
(one or two microphones on camera .. networks taking their feeds from break-out box).
As Steve, WIK mentioned -- these are normally all 3-pin XLR ~ 600 ohm (Z), often balanced.
There have been some commercial product offerings (audio switching only) for amatuer radio, in the past ("pool" concept; or military derivatives) ---
BUT they were expensive ($$) -- enough so that only the DX/Contest operators (SO2R) have "complete package" products today.
You CAN fabricate or do your own DIY Build.
You can get partial schematics from the SO2R operators and ideas from Jim Garland, W8ZR's Station Pro project.
Last edited by W9GB; 03-28-2012 at 05:18 PM.
We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths. -- Walt Disney