wait... common mode signal rejection AND convert a unbalance to balance signal with.... a SWITCH?
You must have misread something there....
I'd love to see something like that done with a switch,
It would most definitely shock the world of electronics if not get you a Nobel prize
Why not just use a transformer for your unbalanced inputs? 1:1 or even 1:2 (will help level balance between balanced and unbalanced channels) is easily found.