I just got a new TV (TCL 55" Roku TV). I’m using Passthrough via Toslink to my old (15 years or so) Yamaha receiver that supports PCM, DD (AC3) and DTS. The TV also appears to support DTS.
But I’ve had odd problems with DTS playback. If I play an AC3 movie, and then a DTS movie, I get no sound. (Amp shows that it’s getting PCM). If the movie has additional tracks, switching to another track (either AC3 or a foreign language DTS track) then the sound comes back. Then I can switch the track back to DTS, and it works fine. The amp at this time shows DTS. I can then play other DTS movies with no problem.
I checked tvservice -a and it shows that only PCM and AC3 are supported. I added hdmi_force_edid_audio=1 to my config.txt and that seemed to improve things, I can now switch from an AC3 movie to a DTS movie and the sound works. But if I play music (mp3 or FLAC) then I lose DTS again.
I think the ultimate solution would be to create a custom EDID file that adds DTS support, but I haven’t been able to figure out a way to do this. (I’ve seen EDID editors, but they are all for Windows and I have no windows systems, only linux)
I do have the options in the TV setup for passthrough to tell it that the amp supports AC3, DTS and PCM. OSMC is also configured to know that it’s AC3 and DTS compatible.
Eventually I’d like to replace the old amp with a modern one with HDMI support, but that’s in the future (unless someone would like to send me one as a Christmas present 
)