I've tried searching for an answer to this but couldn't find an answer, so I hope someone will know. My iMac is currently connected to an integrated amplifier/DAC through the optical output. I'd like to be able to listen to music through the hifi whilst having system sounds etc continue to use the internal speakers. I know that with using the audio output minijack socket that its either internal or external "all or nothing", but would something like a USB DAC allow me to do this, or an alternative software trick? I know airplay would be a way to do it, but it seems daft to buy an Airport Express just to receive AirPlay when the hifi is right next to the iMac.