You can run a extremeHD card in a 1x slot and it will capture upto 720P 60 in 8bit. As we found out :-/
Using the number 2 config in the expansion slot utility should suffice. Both cards require x4.
It should work. If you remove one card and the other is happy in it’s given slot its a card conflict so would suggest as above. Get the latest drivers and firmware.