Some MKV files will only do AC3

New to Kodi and LibreElec.

I am attempting to stream MKV files with DTS audio. Some of the files are streaming in AC3 and cannot find a way to force them to stream as DTS. Is there a reason for this?

I am using universal media server to stream the files to a raspberry Pi 2 running the latest version of libreelec.

Sorted it.
The issue was with UMS. I enabled the option keep dts track in the audio settings under Transcoding settings within Universal Media Server and that enabled Kodi to see the DTS track.