I do not see how that is possible since the board has only one PCI Express x16 bus add-in card connector.
Please look on page 13, section 1.1.2, the slot labeled E.
This board does not have the ability to use multiple connected PCIe X16 video cards, since it has only ONE PCIe X16 slot.
I did not find any PCI or PCIe X1 crossfire cards.
Doc