I came across the above mixer in a school, with digital stagebox on stage. The problem I had was that the preamp knob and HPF knob were non-functional. From the touch screen you can enter a mode by which the knobs across the top all become channel gain knobs, but even then the first few channels were non-functional. I'm least familiar with Presonus, but I can't figure out why these functions weren't working. I searched online and the manual, any idea what I'm missing?