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.  

https://bitcointalk.org/index.php?topic=193695.0

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.

https://bitcointalk.org/index.php?topic=102547
https://bitcointalk.org/index.php?topic=36061.0