Hmmm. I did a sound job for a 5 piece band on Halloween. What we did was mic the drums and run them into thier own mixer and had a stereo L/R out into the PA. The Bass Drum was mic'd by itself into the PA. Then I left the bass drum centered and panned the drums left and right just like it looks to the crowd. So when the drummer did a little roll the sound went in the same direction as the drummer. The guitars were all lined out from the amps to the PA but Mic-ing them although different you could still use the same principle. Since like you we only had two towers for sound. I again panned one guitar mostly left and on mostly right to get them out of eachothers way. The bass was left in the center as was the vocals. It turned out pretty good for the limited equipment. The key was the panning. If you keep everything in the middle. It'll sound muddy and trainwreckish. Yeah up front left and right for the towers.