Let me help you with this.
At this point, our graphics driver supports DTS and it should work just fine with other devices. As first troubleshooting step, I would like you to update the graphics driver by downloading and installing the latest one here:
Also try with a firmware update for the AVR you have and another HDMI cable with better quality. Sometimes cables can also interfere with signals and connection.
thanks for your replay.
In the meantime i found my mistake.
Within openelec i needed to activate the 'advanced settings view'.
Then I was able to allow all codecs (not only DD) to be forwared (passthrough) to my AVR.
Case can be closed
Thanks for sharing this information with us! I am happy to hear it is working.