How do i connect a powered subwoofer to my setup?

so im in ai band and right now we have a powered mixer with two pive jbl eon 15's. we want to add a powered subwoofer and im pretty sure i have to get a new mixer for it(since my mixer doesnt have an output for a subwoofer). Basically i know what i need i just dont know how its all gonna work together. if i get a pive mixer how will my pive pa speakers work? could i somehow integrate my powered mixer in with that? Please Help!! - thanks