I'm attempting to learn my mixer, the Mackie Mix8. When plugging something into the 'tape' RCA jacks, there is audio coming out of the "CR Out" 1/4 ports. When I plug in a Mic, or any other channel, nothing comes out of the "CR Out" ports. Why is that? I'm trying to have the "CR Out" ports connect to my Interface so that I can record different inputs.