I’ve posted about this before, but this time there is a plot twist.
In the past and now, I have never been able to transcode TrueHD 7.1 into anything via my Synology DS918+. Some members told me there is some Intel driver bug blah blah. But today, I rip and play my 1:1 copy of Man of Steel 4K. I tried to use TrueHD 7.1 knowing full well the video would just scramble like usual, but no. This time, Plex transcodes it to eAC3 without a single issue. Wtf? So then I go back to Avengers Endgame and try the same audio thinking that Plex has finally fixed this ridiculous issue, I was wrong. Video scrambled. 
Im using an Nvidia Shield(2017) as the client, with audio passthrough to the Samsung 5.1 soundbar system(Via HDMI ARC). If im not mistaken, this soundbar didn’t even list eAC3 as being supported. It does AC3, DTS 5.1, DTS-HD MA 5.1. I checked the plex dashboard during playback of Man of Steel, it was direct streaming the 4k HDR Main 10, and transcoding audio from TrueHD 7.1 to eAC3. What am I missing here besides Plex still not fixing this issue?