Is my motherboard able to run two graphics cards ? (Sli)

I wouldn't recommend even trying Crossfire on that board, it has no PCI-E lane splitter, so Crossfire would run in x16 x4 mode, leaving your second card badly starved for bandwidth, and likely causing all sorts of stuttering issues. You're best off going for a faster single card, unless you want to get a whole new CPU/Mobo combo that would support SLI/Crossfire and include a PCI-E lane splitter.