I have been reading the forum for some time and also have been mining for a while.  I have one rig with four 6870s and another with two 5830s.  I decided to add a 6990 to my machine (personal use machine not a mining rig) but when I installed it I only see one of the GPUs for mining.  I am running Win7 with the latest Catalyst drivers (11.6 I think) and using poclbm for mining.

Has anyone run into this before?  After searching online for answers I have only seen one post describing the same situation and they claimed that updated drivers fixed their issue.  I wouldn't have purchased a 6990 if I was building another rig but bang for buck since I had my existing system with an open PCI-E slot it was a no brainer but right now it is only performing 340MH/s (I haven't overclocked it yet since I need to get the other GPU working first) which isn't much better than my 5830's that overclocked are doing 300-310MH/s and they only cost $109 compared to the 6990 at $700.  I am expecting 700-750MH/s once I figure this out. 

Any suggestions are much appreciated.