1) I would worry about M-ATX motherboard. It is still just as good as a full ATX motherboard.
2) Here is what the specifications state, which to me says SLI ready...
Intel LGA1156 Core i7 and Intel Core i5 Processors
Intel P55 Express chipset / DDR3 2133(O.C.)
SupremeFX X-Fi built-inSupports NVIDIA Quad-GPU SLI Technology
/ ATI Quad-GPU CrossFireX Technology
3) If you are looking for another board, I would go with the ASUS P7P55D-E Pro
but will cost more.