Audio Setup

Passthrough on tvOS 11.3 is broken by Apple, none of the applications are able to use it.

AppleTV Settings

Apple TV -> Settings -> Video and Audio

Surround Sound: Best Quality Available

Reduce Loud Sounds: Off

Audio Mode: Auto

MrMC Settings

Settings -> System -> Audio output

Number of channels: default 2.0 (stereo output), set according to your receiver/TV setup

Enable passthrough: off

Disabling passthrough will send uncompressed, multi-channel LPCM audio to Apple TV. This results in equal quality sound output, but receiver will not display DTS/DD light