This has been an ongoing issue since June of this year. i have made several comments about it in other groups. A couple of promising replies including yours does not fix the issue. Any channel running DD5.1 for the audio will not work. Even if you do a factory re-set it will down load the required codex and install it but on re-boot it dumps it including your fix. Therefore the only conclusion i can figure is its hardware related and the sound chip is not compatible with DD5.1.
I've tried this fix twice and both times the sound doesn't play using a MKV file with 5.1 and I also tried using DOL1 and DOL2 on a channel I know has 5.1 and there is still no sound.