I have the z77a-gd65 and i cannot get 5 cards to run...always have 1 card which shows up in windows but has a code 43 problem...with win7 enterprise x64.
Try Windows 8. Seriously...it has been reported to support more cards.
I've only heard issues regarding Windows 8. My friends and I couldnt get the G45 board to accept 5 cards on it and we even used presence shorts.