Here's the skinny on the digital output on most tvs:
If you are using the internal tuner(ATSC), then you will get DD out of the output. If you are connecting an external source like and STB, or a BD player, etc...most will not pass the DD audio out the optical port, but will pass Linear PCM...thats the way its been since the beginning. If you are looking for DD sound from an external source, you must run the audio out of the external source to your sound system...
That's a great explanation, thanx.