Still can't connect more than 4 cards on my H81 BTC Pro Board. Five or six cards trips a reboot right after i start ccminer.

rolling back nvidia drivers, maybe that will sort it out.
I have the same problem with Linux, but not every H81 BTC Pro board. ccminer crashed when using 6 cards and only with a few algos, e.g. JPC,NIST5.
X11 works without problem. So I found out that not every H81 BTC Pro Board has the same build quality. The reboot indicates that something wrong with the power connects to the board.
I know it's really stupid but I tried a lot of combination last months to find the problem. (I have 6 H81 BTC Pro boards).
Some recommendations:
1. Change your board
2. Change your cards, some cards are heavily manufacture-overclock and cause trouble with the main board.
3. Riser could be a problem too.