Due to license and other rules this passthrough is quite rare. Sony as you guess holds more patents and seems to pass more HD audio streams.
I wish I could have guessed your setup but failed. Also, there is no rooting Smart TVs today.
If the source is HDMI then audio extractors are used. Example at https://www.amazon.com/ViewHD-Extractor-Optical-Converter-VHD-H2HSAs/dp/B00KBHX072
I recently bought a UN55MU7100 Smart TV which, doesn't provide me with an option to pass through audio through HDMI as is. It provides with option to turn the audio signal into DD5.1, DTS or DTS Neo. I must say TV does a horrendous job converting. I would rather have the TV to pass the audio to the receiver unmodified, as the receiver does a better job at playing audio; be it in the source format or by converting it to another format. It definitely sounds much better when receiver performs the conversion as opposed to the cheap codecs used by Samsung.
I have tried both HDMI and TOSLINK, both work the same way with no passthrough.
Is there a way to get the TV to bitstream the audio to the receiver. I don't mind optical over HDMI, but I need passthrough. Otherwise I might just return it and buy a Sony.
Just to add I do have the HDMI cable connected to the ARC port on TV and my receiver does support ARC. The fact that my receiver can play audio from TV proves ARC is functioning.
I don't mind a solution that requires hacking or rooting either.
Thanks for any help.

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