I have the same H81 BTC board, and running win7 x64 it wasn't too hard... Not sure if you are on Win or Linux.

I was running just 4 cards for a few weeks, but when I went to add the newer two cards, I added them one at a time, and just rebooted it a few times.

The 'finding new hardware' process took forever to complete, but I just let windows find each card, then I started up the miner, saw that it was working, and then went about adding the 6th one the same way.

I did have to roll back a driver once after I installed it and it made mining slower, and that was essentially the same process, because when I fully removed the driver, all the cards went to discovery and re-installed using the driver that comes with the OS.

Then I stepped up to the newer Nvidia driver from there.

Hope that helps.

I also have EVERYTHING plugged in... all the MB plugs and powered risers using unpowered cards.