No Yamaha number so supply that so folk can be sure what is possible.
While some TVs have audio output on optical or other, it's rarely more than stereo and some block audio passing when the source is HDMI.
So let's get the TV model number too. Since you have it going to the Comcast box, may as well tell all the numbers.
Even with all that , Comcast may have to tell if it blocks HD Audio.

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