Transcoding DTS to Dolby Digital is not supported in HiMediaplayer.
It can be done in Kodi though with Kodi internal player. By using Kodi internal player you'll not lose much in terms of picture quality. Most formats play the same as with Himediaplayer because Q5/Q10 Pro supports OMX (giving native hardware playback). What you'll lose is 7.1 audio (irrelevant to you anyway), picture adjustment settings, and marginal performance at very high bitrates.
To transcode everything in Kodi to Dolby Digital AC3:
Change Kodi settings to Expert.
In Kodi, go SYSTEM - Settings - System - Audio Output and set:
* Speakers to 2.0
* Enable AC3 passthrough
* Enable AC3 Transcode
* Disable DTS