Atikmdag patcher used to handle driver signature when you mod your cards, also to increase refresh rate and pixel clock, if you didn't mod your cards, you didn't need it. Windows 10 latest fall creator update 1709 would help you.
Do you disconnect all GPUs apart from the x16 slot when installing new drivers?
You could plug at least one card when installing the driver, or you can manually install/update your cards using
Package folder.