I have a small PA that consist of two Behringer 400 watt powered speakers and a Tapco Mixer. The problem I'm having is channel one works fine but channels 2,3 and 4 don't get loud enough to hear over the band. Is there something wrong with the mixer or is there not enough power to use more then one vocal mic? Could I use a power amp with the powered speakers to give it more power? Also should the volume on the speakers be turned all the way up? Right now they are at half, I was thinking they should be turned all the way up and control the volume from the mixer.