|The i5 750 sells for about $200 & the board you mentioned goes for about $140. 4GB (2 x 2GB) of DDR3-1333 goes for about $90.|
Dual means two, so if you want to enable dual channel mode, you need either two matched sticks or two matched pairs of RAM. Using either one stick or 3 sticks will cause the system to run in single channel mode. That particular board doesn't support triple channel mode.