You can assign anything to the Monitor Output port.
Why not just assign the Talk back mic to an Aux? Then have one of the 40 sources being selected in the ME-1 as an Aux input and you have Talk to the ME-1s at that point.. When you press the Talk button on the console it would route to the ME’s
My guess is if you are using ME’s you probably dont need as many aux’s live in the mix so you could assign different Aux’s to the groups of ME-1’s or just have all ME=1s have a default access key to pick up TB.
Will that work of for you?