4 ATI saphire 290 settup

[kopam]

Okay guys i really need some help.
I got 12 Ati Saphire 290 a few days ago.  At first i was thinking of building 3 rigs with 4 cards each. However right now it seems impossible.
Here is my config :
mobo - ASUS FMA85-V PRO
CPU - AMD A4-400 APU
RAM - 4GB
GPU - 4xATI saphire 290
PSU - 2 x 750w
PCI-E EXT - 1x-16x with power


Okay so first of all, please tell me what do you think of all parts. Should i change anything ?
Right now i am having a shitload of problems ... cards are shutting down, even the second PSU is shutting down sometimes.
I understood that the PSU's are not strong enough. I am measuring ~750-760 on the 1-st PSU where its 2 cards + mobo etc. Each card is consuming about 330 watt + mobo etc. So this i think this is the first problem.
I am about to get corsair 1200 platinum so this should fix this problem.

So pretty much please tell me what is the best config for 3 ( if possible 4 290 ATI saphire cards ). Right now i have the feeling that PSU + mobo can not handle the 290's and they simply fail. If i have to i will run 3x on each mobo and get 1 more but do you think the problem is simply in the PSU or maybe the mobo/CPU/RAM  also make problems ?

Please help me, its soooooo frustrating to have 12 cards and not to be able to mine with them !