The original Xiaomi Mi Box was the only affordable certified Android TV device with Dolby TrueHD and DTS-HD Master Audio passthrough support, but it was removed in Android 9 by Xiaomi due to licencing restrictions.
It appears though that multichannel PCM support was also removed as stated by u/Tomahkin in its own post .
I was able to confirm this by connecting my Ematic Jetstream device (also with Android 9) to an AV receiver and it didn't play multichannel PCM either, instead, it was downmixed to PCM 2.0.
Looks like Google removed multichannel PCM support or this is a bug plaguing every Android TV device where Android 9 is installed (except of course the Nvidia Shield), either way, this is unacceptable. 😡😡😡😡
SmarTVs running Android TV with or without eARC don't support multichannel PCM with internal apps so they don't apply to this situation.
Does Android 10 support multichannel PCM or is it gone for good?. The Chromecast with Google TV, the Mecool KM1, KM3 and KM9 Pro are on Android 10, so I hope someone with any of those devices confirm this.
Please, share your thoughts.
I don't think all Android 9 devices are affected - I have a new Sony Bravia XH85 that decodes TrueHD to multichannel PCM from Kodi just fine. My AV receiver doesn't have eARC so I guess it can't handle TrueHD and DTS-HD via passthrough but I'm sure if I buy a newer soundbar it would work fine.
The only other android-based player I have is a FireTV 4k which (when directly connected to the AV receiver) will also send TrueHD and DTS-HD-MA as multichannel PCM just fine from Kodi. Having said that, there's been talk that the latest update to FireOS (6.2.7.6) transcodes everything to DD+ but I haven't tested it yet.
EDIT: After the new update the firestick behaves correctly when plugged into the TV but transcodes everything to DD+ when directly connected to the AV receiver :-/