I have a system with 3 6990s in at once. They work fine solo, all three work for graphics and OpenCL.
I understand I can't put all 3 in crossfire together (each card only has one connector), but I'd like to get 2 of them in crossfire. This doesn't seem to work using the 11.8 Catalyst driver though.
If I attempt to connect the crossfire cable between card #1 and card #2, or #1 and #3, opening CCC causes the display driver to repeatedly crash. If I hook #2 and #3 together, it opens but the diagnostics page tells me I've connected the cable incorrectly.