tl;dr
Plex on Mi Box lose DTS support/DirectPlay on DTS files after Oreo update
As most of you guys know, Mi Box does support DTS.
But playing DTS thru Plex has been a trouble for a long time coz it makes Plex Server (PMS) to transcode for every single time Mi Box need to plays movie with DTS.
But somehow this issue has been fixed for a while. IDK when it was resolved exactly... at least for the past 3 months, it works perfectly with DTS movies.
Until the Oreo update came, after the update all movie with DTS have to, again, be transcoded by PMS.
If you use not so powerful server, like NAS, (so you gonna need DirectPlay to works) and have a lot movies with DTS audio, then I suggest to stays on Mash-mellow, at least for now.
Here is an example of this issue
File : The Darkest Hour (DTS audio)
Mi Box (Oreo) Transcoded
https://i.imgur.com/5AQQAtfl.jpg
Mi Box (Mash-Mellow) DirectPlay
I was the exact opposite. DTS wasnt working in 6.0 and plex transcoded the audio. Now it is working in 8.0.
Using SPDIF cable to my receiver. Audio set at RF. Surround always on.