Well, so to say, the question is in the title 
I ordered PC with this motherboard and one Radeon HD 6790 graphic card. I believe, it should be supporting only one, but i can not be really sure as seeing the MB layout. I am very bad on hardware part, so its kinda hard to get it.
CPU Intel Core i7 3820
And currently 550W Power, where i am sure it wont be enought. But my question is mainly, can i upgrade to two GPU's if possible. Main reason: i saw that tho gpus perform not that bad + this one isnt expensive as top tier GPU. And other reason, i am not hardcore gamer, but sometimes go for some heavy games and i dont want to leave them just because of serious lag.

I ordered PC with this motherboard and one Radeon HD 6790 graphic card. I believe, it should be supporting only one, but i can not be really sure as seeing the MB layout. I am very bad on hardware part, so its kinda hard to get it.
CPU Intel Core i7 3820
And currently 550W Power, where i am sure it wont be enought. But my question is mainly, can i upgrade to two GPU's if possible. Main reason: i saw that tho gpus perform not that bad + this one isnt expensive as top tier GPU. And other reason, i am not hardcore gamer, but sometimes go for some heavy games and i dont want to leave them just because of serious lag.