I did the same for my Ncore amplifier, based on a preassembled board from Electronic Salon
https://nl.aliexpress.com/item/1981878470.html
The relays used should be high quality (gold plated silved alloy) and are make-before-break avoiding (most) of the clicks. Ground will have to be common but all the rest can be switched with a 12V trigger from your receiver/processor.
It does need a 12V regulated power supply but that's also easily found.
Basically then you add & solder 4 XLR inputs and output to your amps, and include a 12V 3,5 inch mono jack for the trigger input.
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