Just went through this tricky exercise and thought I would post the solution. I have a projector that takes HDMI but obviously doesn't have audio. I wanted to run optical audio to my receiver but the Motorola DCH3416 wouldn't let me do it. It defaults to sending the audio through the HDMI connector. Hmm. How to get to the magic menu to change this setting?
If you press the menu button, you get the Comcast menu which doesn't let you make this change. What you want is the system menu. To access this menu, press the power button on the box, and then press the menu button on the box. I know sounds weird pressing menu after allegedly turning off the power, but it works. No you've got a boring black and white display. Select the HDMI configuration, and then under audio change the option to L-PCM. Works like a champ!
Hope it helps and saves someone some headache. Great forum. Love you guys... just not like that - Kevin