You are not alone. I'm having the same problems. I have 2*6990 cards and havent been able to use any of the new 14.X drivers, the 13.12 is working fine tho.
When I install 14.X driver and reboot the machine only 2 or 3 of the adapters are detected. (catalyst -> information -> hardware -> check the linked adapters, if the memory/gpu speeds are not show for the adapter, the card is not properly detected).
I've reported this via the problem reporting process to AMD, but have had no reply.
Would be great to have some sort of an comment from AMD. I've spend quite significant amount of money on high end cards which are not now working properly with the latest drivers.
I'm willing to provide more information and logs if needed.