Before I forget this thread has some great people on it that can be super helpful in these situations. It's in the Alt coin mining section; normally I would say search or create your own topic there but it's tough to navigate at the best of times.
https://bitcointalk.org/index.php?topic=3843565.0
To try and help you here. Are you only trying to boot Windows to MOD the cards? Or are you planning on running Windows permanently?
I'm no expert I run 1 rig, and have swapped between HiveOS and Windows which is where I stayed for what I'm mining at the moment. It would be awesome if your Smos where on a USB ( you only need 8GB I think) and you could just have the SSD loaded with Windows and swap between them freely that way. Is that something you could do to make your life simpler??
If nothing else when you turn on the rig you should just have to hit Delete key if I'm not mistaken to access the Bios from there you can select the what to boot from.