[noggin]

This is all I set in LibreELEC Kodi Audio Settings:

- Channels 5.1 or 7.1
- Best Match
- And I can leave all passthrough audio options on. 
5.1 / 7.1 AAC audio get's decoded to 5.1 / 7.1 PCM as confirmed by my Yamaha AVR and all Passthrough audio works. 

So LibreELEC will output PCM to the receiver?  

 Yes - multichannel PCM is supported on (some/all?) AMLogic platforms - and so AAC can be decoded to PCM multichannel, rather than requiring a transcode to Dolby Digital 5.1.  The same approach is used for WMA and FLAC multichannel audio (and possibly multichannel DSD SACD stuff?)

AIUI there may be an AAC bit streaming protocol defined for HDMI audio now - but it's not supported by mainstream amps (at least not yet)