I need to connect a powered mixer to an amp.?

I have a PA system at my school that we use for dances. I DJ here and I've been having trouble hooking up the speakers. We have 2 Large JBL towers and a large JBL Woofer. Currently, I am only able to use the two towers because the back of the powered mixer only has 2 NL4 ports. We do have about 4 separate amps but I'm not sure how to hook the mixer into the amps and then into the speakers so that I can use the subwoofer. Any help would be greatly appreciated.