Your motherboard has:
1 x PCIe 2.0 x16
1 x PCIe 2.0 x1
1 x PCIe 2.0 x4
Which means it actually can support 3 GPUs if you use an adapter like this:
http://www.ebay.com/itm/PCI-E-1X-to-16X-Riser-Card-Flexible-Extender-Cable-Cord-Molex-Capacitor-/281257445352
It can support even more with other hacks but they aren't as cheap.
Brilliant, thanks for the very helpful reply. I really appreciate it.1 x PCIe 2.0 x16
1 x PCIe 2.0 x1
1 x PCIe 2.0 x4
Which means it actually can support 3 GPUs if you use an adapter like this:
http://www.ebay.com/itm/PCI-E-1X-to-16X-Riser-Card-Flexible-Extender-Cable-Cord-Molex-Capacitor-/281257445352
It can support even more with other hacks but they aren't as cheap.
Will the cards run smoothly using these adapters at normal hash-rate?