crossfire supports Sli but Sli doesnt support crossfire.
That's not true at all. Maybe you could get a Crossfire board to run SLi if you find a hacked solution for it, but there's no guarantee. If you want SLi, get an SLi board or, if you must, one that is not officially SLi but has been proven to be able to run SLi. Same for Crossfire.