Hi Scott, Are you mic'ing everything up or just vocals and kick drum? We run a Yamaha mixer through Mackie SRM450's and found that if you keep the speakers set at "Unity Gain" the top-dead-centre setting (should be marked with a "0" and have a physical "click"), keep your channel gain setting down on the mixer and control it all through the sliders, then you shouldn't get too much trouble with feedback. Also, your mics must be positioned behind your front-of-house speakers, otherwise it'll feedback like a bastard. Bring your levels upgradually and remember that harmonics and clarity are better than volume and gain. Behringer mixers are basically functional clones of the Mackies and are very much a hit or a miss regarding quality. I personally don't rate the newer Class-D Mackies either, though they make good stage monitors - but not as good as the old Laney one I sold you yonks ago I'd be inclined to invest in a better mixer - I've had Yamaha, Peavey, Mackie, Behringer and Soundcraft mixers over the years and I'd say that the first two were the best.