Multi Graphics card setup help

[cakey]

I have been mining with a radeon 6990 but decided to add a radeon 7770 and dual card mine.  I installed the second card but cant seem to get it mining.  i currently am using phoenix miner 1.7.5 dose anyone know if theirs something i just don't know? (their is much i don't know).  If someone could help me get this running it would be much appreciated.