So I'm getting the impression that the outputs (8on the back) aren't powered. I have my monitors plugged in to 1-2 and they work beautifully. I planned on having multiple headphones plugged in the other 6 outputs because I'm recording with a few other people. However when I plug headphones in to the outputs, nothing happens. Do I need a headphone amp? Is there an easy fix that I'm just blind to?