I have 2 Asus HD7960 video cards that came with version 9.2 drivers. I have 10 monitors working fine with Windows 7.
When I upgraded to Windows 10 only 9 monitors worked. Then I installed version 15.7 drivers. Still only 9 monitors.
I went back to Windows 7 and all 10 monitors are working. Then I installed version 15.7 drivers. Only 9 monitors.
My mainboard is Asus Z87-WS with Intel i7-4770K cpu.