The Macbook Air (2012), only has one 1/8 audio output. My DJ program can play audio on one channel (for example, play "song A" through speakers) while at the same time playing something on a separate channel to a different output device (for example, playing "song B" through headphones. Does anyone know how I could possibly do this, if possible at all? USB to audio? Some kind of external sound card? Any ideas?