I have two rigs with 5 7950s one using the 970 EX4 and one using the 990 EX4.  Theyre both the same.  You just have to figure out which combo of risers, no risers, powered risers, not powered risers, short/no short presence pins, which card to hook monitor too, etc.

Any more than 4 cards HAVE to boot into failsafe mode.  4 and under and you can boot regular but over 4 you need failsafe.

Took me almost a week to figure it out thats why I havent touched my rigs in months.