I have a Bose speaker system connected to my iMac 27" via USB. I've purchased a device that allows me to play my XBOX through my iMac 27" using it's mini display port. It works but the XBOX's audio is coming through the iMac's on-board speakers instead of through the connected Bose speakers. All computer sounds still come through the Bose. How can I separate the audio and redirect it so that it comes through the Bose speakers like everything else on the computer?