When you use the 3 sticks ram in a dual channel board then the ram is in single channel mode. In your case it will be fine, because the different performance between dual and single channel is small, you can't notice in the real usage. Read the reviews.
You can use "tri-channel" RAM but the mobo is dual channel. To quote the specs: ■Supports Dual Channel DDR3 2133(OC). Don't waste money on tri-channel as you need to pair sticks of RAM. Go with either 2 sticks or 4 sticks of RAM.