I'm not arguing. Just trying to help out.
I'm not sure about which slots you need to put them in to get 16x/16x, that will be somewhere on the ASUS website. But, the Antec 1200 case only has 7 expansion slots and so that means the cards will have to be in the two blue slots. The cooler of ASUS ENGTX580 DCII only takes up 2.5 slots according to Asus (I cannot reference this, I just read it in another thread), but the actual card takes up 3 expansion slots of the case. If you buy lets say a HAF X, you will have 9 expansion slots which would let you use any two PCI Express x16 slots for the graphics cards.