I used the USB out of the Mac and directly into the DAC2. The sound of the USB was somewhat better than the Sonos, but the difference wasn't huge. Maybe it has to do with the way the ESS chip copes with jitter, which is the Sonos' weak point. In any event, the big advantage to using the Mac/USB is that it allows me to multiply the benefits of 1) asynchronous data, 2) high resolution files, and 3) Pure Music's memory player (with iTunes).