The 6950s Crossfired under max load draw about 329W or ~28 amps. on the 12v rail. The 560s in SLI under max load use about 298W or ~25 amps. The Corsair TX750 offers up to 60 amps. on the 12v rail so you should be fine with either set-up.
First, I admit right now I didn't look up the mobo. I am at work XD
But, make sure it has 2 PCI express ports, I am guessing the cards you mentioned are PCI express, I think they all are now a days.
Second, look at the cards you want to put in. A large number of cards require additional power, 6 or 8 pin connections. You'll need to open your case at look at the power connectors. See if it has any of the power connectors your new Video Cards will require.
Last, Check the specs and reviews of the cards if possible, some Video Cards will come with adapter's to make a standard 4 pin power connector to the correct power. Usually the 4 pin to 6/8 pin adapters that come with cards require two 4 pin power connections; look to see what one, if any, come with the card.
Once you get the Video Card info from the web, the actual physical check of the connections will take all of like 10 seconds.