You can only use two of the four channels. You will have 4 terminals per two channels right!
LEFT + LEFT- RIGHT + RIGHT-
So you are goint to use the LEFT+ and the RIGHT- to bridge it. So that is what you run to the sub like I have it drawn. The other two channels arent going to be used unless you have another sub
*NOTE* I have heard of people running all four channels to a dual coil sub. I have never did this so I can recommend it. Ask someone who make have done that type of setup before