Audio Issue Xbox one and Clients

I am still having issues with Xbox One and Audio, My Audio receiver is a Meridian G68 and my xbox is connected via optical my G68 accepts DTS & AC3 passthrough and the films work OK (Most of the time)
However I get serious issues with music still, Plex does not like 4.0, 5.0, 5.1 and 7.1 multi Stream Flac files sent via either HDMI (Tried with a HD621) or via SPDIF

This is not my equipment as I have tested it from the HDMI /SPDIF & COAX from my laptop and it works OK
I have ripped a load of DVD-A 24/48k and some 5.1 24/96 and the plex just wont play it back or down mixs to stereo??

Albums Most of the porcupine tree DVD-A and DVD ripped as 5.1 Flac
Pink Floyd 5.1 DTS - 5.1 Flac
Jethro Tull as above
Flaming Lips Yoshi battles the pink robots DVD-A ?

none of these rips are encrypted or have drm on them

I have 200+ Hi Def albums to place on my plex server and it frustrating that music still is iffy

I have just seen the bloody XBox transcode 5.1 flac to stereo MP3 WHY ???

Currently the app is limited to MP3 and M4A for music playback:
https://support.plex.tv/hc/en-us/articles/203824396-What-media-formats-are-supported-

While the Xbox One does support DTS, It has not been released to 3rd party app developers so the only app able to play DTS is the official Microsoft media player.

Flac itself is also not listed as a supported format by Microsoft, so until Microsoft adds support and releases it to 2rd party apps it will always need to transcode.
http://support.xbox.com/en-US/xbox-one/system/media-player-faq

Thanks for that Info jmckee, However I also tried the Xbox media player and that was also down mixing to stereo, I assume this is because Microsoft are ■■■■■ and don’t support developers or High end Video/Audio standards, I suppose there is no surprise there. So what device can I get that will allow all 6 channels of Hi-Def. Audio ? or am I going to have to get a linux/windows box with plex home theatre. I understand Plex.tv engineers frustration with Microsoft, they have built a great piece of software and watch it get crippled by Microsoft,

I think currently the best setup is some variant running PHT.

I don’t know too much about it, in my house the Xbox One is in the main room and I have Fire Devices for the other TV’s. Unfortunately, we don’t listen to a lot of music through them so I don’t have a lot of experience with it and couldn’t really offer better advice for it.