KA7OEI has written an article detailing a simple 8-channel receiver voting controller:
To simplify things, this voting controller sits in “front” of an ordinary repeater controller, taking the audio and COS inputs from the various receivers and outputting a single audio and COS signal.
If the repeater system in question uses subaudible tones, it is recommended that “discriminator” audio (e.g. that which has not been de-emphasized) that has not been subject to a squelch or tone detector audio gate be applied to the voting controller from the link receivers as well as any “local” receivers as this will assure that the voted audio will contain the subaudible tone.
More details on KA7OEI ‘s blog.