Saca el audio por el mismo cable HDMI
Tambien puede sacar el audio por 5.1

The Mini DisplayPort w/ 5.1 Channel Audio to HDMI Adapter lets you connect a high definition monitor or television, to a Mac Pro (2009), Mac mini (2009), iMac (2009), MacBook, MacBook Pro, and MacBook Air with Mini DisplayPort.
Combine Full 1080p HD mini DisplayPort output with 5.1 channel audio output from your Mac in a single HDMI connection to your TV or other HD display.