Optimizing .mkv playback with DTS-HD sound

I’m using Kodi for a few years now. So far I never ran into any serious problems I couldn’t solve.
But since I’m replacing every movie and tv-show with my own .mkv files (direct uncompressed version from the dvd/blu-ray), I’m having trouble playing everything with a resolution of 1080+ together with DTS-HD 7.1 sound.
So far it seems it is really just the sound causing the playback issues as everything else with “lower quality” audio plays just fine.
The problem is as following: The movie loads just fine, plays as expected during the first X minutes (up to 15minutes sometimes) and then the audio goes silent for a short time and then just stutters so that you can hear only a few words every now and then. The image plays along just fine. If I pause playback, everything is fine again for several minutes until it all starts again.

I already tried changing from analog to HDMI output, enabled and disabled passthrough but still no difference. I would think that the cubox4x4 has enough resources for that. It’s running openElec v7.0.1 (imx6arm) with Kodi 16. I tried v.6 of OE as well.

Any ideas why these specific files are causing problems and how I can optimize the playback?
thanks