The music is going through a large speaker amp. I am trying to get the metronome click only in the headphones, and not through the speaker (with the rest of the music, what the listener can hear). I'm not sure what you mean by what setup and interface I am using. I am running on Mac OS X 10.4.8, and am only using my iBook G4, the speaker, my headphones, and the subsequent cables (all 1/4 inch or 1/8 inch) as equipment.