The issue isn’t the cabs. You don’t need more cabs, you need a better sound guy. I’m going to assume you have the guitars amps are mic’ed? As for your rig, if you are playing for 350 people and don’t have your bass through the PA, 300 watts and two cabs will barely cover it. 2 Cranked 200 watt guitar amps is enough to bury you , the vocals and most of the drums.