I'd try a fresh reformat^. It didn't work with 6 cards my first try until I did it on a fresh install. I see you're in thread but here it is for anyone else that would like to know. 
Also make sure to know if your board needs a presence short on any of the PCI-E lanes, my current board did need one to get the 6th card working.
Also make sure to know if your board needs a presence short on any of the PCI-E lanes, my current board did need one to get the 6th card working.
This is a fresh win8 install. And none of them appear to need a presence short, as they all appear in windows (and in catalyst - where it says one card is "linked"), so I know they're recognized -- but this error 43 thing prevents the 6th card from working (a driver thing)