So basically I have my macbook pro retina hooked up via USB to a DJ MIDI Controller, I've got all the drivers installed correctly and stuff. But there's a problem. It plays music through my DJ Controller to my monitors just fine, but the point is I can't control the volume because it has no ''output controls'' or something.. There's an O with a slash through it when I try to adjust it, the music is just deafening now. Please help me...........