I've got some synths connected to a mixer, which I've got going into my Mac's line in. It hears it fine, and I can record what's coming in via a wave recorder, but I want to be able to HEAR what is coming in too. I mean like, have it playthrough the computer and right to the speakers. Any ideas? P.s. I went to Audio Midi Setup and the Playthrough button in not check-able.