I'm using an MBR partitioned SSD with win7 and it works with 7 nvidia gpus. On the asus prime z270-p offcourse.
I was under the impression that Microsoft used MBR by default on all windows installs. So why would i have an MBR issue to recognize additional cards.
My AB350 board did 6 cards (not of the same brand), my asrock does 8+2 and now this Asus prime Z270-a only does 3 cards of any type. All systems are running off a normal laymen's install of windows.