Hi - I'd be interested to know what the outcome of this issue was? I have the same problem.
I have the same problem on my new Pansonic screen. Excellent in every other respect, the PCM (stereo?) down-mix does not appear to work off the television. Anybody had success with an adapter going from Digital audio into digital audio? I don't particularly want to revert to using analogue inputs on my hifi.
I bought a Lindy Dolby Digital converter, have not found anything that will do a Dolby Digital to stereo PCM converstion (and would also need to passthrough PCM). It's a little white box powered by usb that takes the optical in and outputs 2 channel analogue via RCA. Functional and sits in the cabling but doesn't quite fit with my other hifi kit, amp needs turning up over 2-3x to get the same volume when using that input.
This is a real pity for me, I really like the TV except for this issue. I wouldn't mind if it just ouptut nothing if an app writes Dolby Digtial and you've set the output to PCM, but it sends down a signal that causes a really terrible and loud sound to be played which means I cannot have the TV connected to my hifi dac at all just in case someone opened Netflix or Amazon. The TV can decode Dolby Digital as it can play this though the internal speakers and there are not 5.1 speakers inside so it is down mixing, doesn't mean it would be able to output this via the optical out though.
I have been looking to upgrade my amp/dac/speakers and because of this I tried looking for something stereo ( I only want 2 speakers) that would decode dolby digital. The only match I've found is Arcam's SR250 but this is over my budget and has much more features than I need (video for starters). Would make much more sense to replace the new TV with another brand and select from the huge choice of stereo equipment.
I found another similar thread describing this issue on another site and the most recent comment said this had been fixed for the Amazon app and yes I can now have the audio through my hifi DAC when watching content in the Amazon app.
I updated the TV applying the HDR update a few weeks ago, perhaps it's also automatically applied other updates.
Just Netflix to go now.
... and still no fix from Netflix...
Ignore me if this has been mentioned / or is irrelevant (as the thread is a couple of years old!)
But I think I saw someone mention that the Panasonic TV did not have an analogue output.
The good old SCART socket gives stereo analogue out.
It'll be the TV. I have a Panasonic connected to a Sonos using the optical out and that sounds terrible too.