I dont know if anyone has run into this problem before but I figured I would rant/pass along what we went through. I have a 14 channel mackie, bought it used of CL package deal with a QSC GX5 and Peavey 215's. Its a pretty decent set up for the size of venues we play. We were constantly fighting being loud enough. At first we thought it was just because we were running monitors and mains through the GX5. Which is part of the case.. But even just the mains we would have the amp cranked, trim/gain at 3 o'clock on mics, and the levels set way above unified. We were still getting a muffled sound and feedback nightmare. So before we were about to throw down a pretty penny for a new amp, I took our set up into our sound guy to check the power output on the mixer. We thought we could have blown a tweeter blah blah etc. So we are messing with it and he says "This is the dumbest button ever put on a mixer". The mic/line switch was turned on... I never even knew the button was on the back of the mixer (being new to live sound game). Basically we were trying to play through a mute button. Night and day difference... Now we can have the levels set at U, trim about a 10 and now getting double the output we were before. Would have been nice for the seller to pass that info along when I made the purchase...