Which version of Windows? Windows 10 should handle up to eight GPU's per driver, so eight AMD cards + eight Nvidia cards.
thx, win10 is 8gpu working
but I add 9 gpu , windows 10 crashed when start mining...
did you have to do anything specifically to make it work you would share?
i have one of these boards coming tomorrow, i am also planning an 8 card build and just trying to do my research here hehe