[wrxtasy]

You could try hard selecting HDMI in Android settings > Sounds > Digital Sounds > ...

I don't have this box but I bet Technicolor have not bothered to add compatible Kodi Krypton IEC61937 audio passthrough code into Android Firmware.

You will have to use one of the Krypton (audio) shitty versions from here if that is the case:
http://mirrors.kodi.tv/test-builds/android/arm/