Its not supported by the motherboard. You could try - http://www.overclock.net/t/601955/sli-on-xfire-motherboards-confirmed
But it could result in your mobo being useless. I wouldn't. I'd get another mobo. In fact I wouldn't have bought that mobo with that restriction in the first place.
Makes sense, thanks for the fast response, might look into the workaround, and yeh I regret my choice of motherboard after the fact, kind of rushed into buying it.