When HDMI-eARC first rolled out, no TV apps passed high bit rate audio via HDMI-eARC. The TV would only pass the audio for external devices connected via another HDMI port.
For example:
Plex app on a Smart TV: No TrueHD via HDMI-eARC. Limited to what passes over HDMI-ARC.
Plex app on a Shield connected to same TV: TrueHD passed via HDMI-eARC.
AFAIK, the above is still true. I have not seen any posts on this forum that would indicate anything has changed.
Just an FYI before you drop some money on new sound gear.
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