Let's move it to the Toshiba thread, as others with the same TV will also be able to help you out.
From what I see, in your setup, the TV shouldn't be any bother while playing DD audio from firestick, right? Firestick is directly plugged into the AVR. With TV's internal apps, you will first of all need an ARC compatible cable in HDMI 1 to ARC port of the receiver. Then you need to experiment with the audio options in the sound menu (auto, PCM, DD, DD+).
I'm currently using optical audio for my 5.1 speaker and all modes work exactly as expected.
WHen playing through firetvstick, I am getting DD 5.1 audio
I was not getting DD audio when playing directly on the native Apps. However, I could change the sound setting to DD in the TV menu and it worked fine. Surprisingly, the auto/passthrough/DD+ nothing else worked, not sure why
Anyways, I am done with the crappy OS and interface. I should be getting the fireTV stick 4K soon (managed to get one free )
I tried with the same settings mentioned by you with little changes here and there and I am very happy with the PQ. Even the full HD videos look pretty good to me. I have not seen any issues with motion yet. but need to see with sports
Mods, please close this thread