I got both of my cards running. It turns out I had to connect a monitor to each card and I used the Catalyst 13.11 drivers.
Have you tried the config I posted?
And don't forget to batch start cgminer with:
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
You can also trick it to think there's a monitor plugged in with some 1/2 watt resistors.
http://www.overclock.net/t/384733/the-30-second-dummy-plug