The audio output from the audio system isn't PCM format even though the TV Digital Audio Out is set to PCM
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The TV lets the audio signal input from the HDMI® source device pass through as is when eARC mode is enabled. Therefore, the sound output from the audio device is the same format as the audio signal input to the TV, regardless of the TV's Digital audio out settings. For example, if the input is 7.1 channel linear PCM, the output is also 7.1 channel linear PCM.