Are you using the Sony's internal tuner for audio? The Motorola box indicates that you aren't using a CableCARD, and there's no built in HD tuner for over-the-air HD broadcasts. Unless I'm mistaken, you won't really need to get audio out of the Sony - it can potentially spend almost its entire life set to the HDMI input (except for occasional trips to whatever input is connected to the 990's monitor output for access to the 990's setup menu) and serve solely as a video display.