It may depend on what Mac we are talking about. I have an iMac and I'm using an Apple Airport Express to feed my 990 with a digital optical signal for iTunes playback. For combined audio/video it sounds like you've figured out the video. I'd use the digital optical (same jack as the headphone) output on the iMac to feed the Onkyo with digital audio. I have no idea how those two signals would sync up but that might be a solution.