Can you connect any kind of pci express card to a pci-express x 16 slot
As long as they are x16 cards they are both compatible with x16, despite the Manufacturer.
You may want to refer to the board manual, but I think if you want to use a single vid. card in a cross fire/SLI board, you have to use a determined slot..ie: only one of the two slots will work for single card setup.... Might want to double check on that as I said