I was under the impression that the xbox one Plex app would direct play MKV with Flac 5.1 and convert 6.1 and 7.1 to 5.1. But a quick look on the server shows the audio is being transcoded??
Intel® NUC Kit NUC6I3SYH
Xbox One S
Meridian 861 : Meridian HD621 : Meridian DSP5500 FCR
Qnap TV-S 471, Qnap TS-871