My friend just bought a powered subwoofer and we're having trouble getting the dang thing to work. He's got a behringer Ub222fx-pro powered mixer set up. when we run a 1/4 inch speaker cable from the amp's sub out to the sub woofer we get a pretty faint signal through the sub woofer. definitely not as loud as it should be. on the back of the speaker where you plug in the speaker cable all the 1/4" inputs say line in and line out and they also say satalite/sub woofer. what does this mean? our collected knowledge of PA usage is limited. Can anybody help us?