I have some equipment i would like to see if i can run together. I currently use a Behringer PMP2000 with two passive 15" mains for our small/odd no House PA gigs. I also have a passive 18" sub that i would like to add to the setup. I have a separate power amp and crossover. Am i correct assuming the sequence on connection is powered mixer-power amp-crossover-sub? Any advice would be greatly appreciated.