2015-11-12, 10:11
The DTS-HD limitation is a Raspberry Pi limitation, and the only way for the Pi to output DTS-HD is to decode it to PCM. OpenELEC v6.0 now supports outputting DTS-HD as PCM for all devices - not just Raspberry Pi - as an alternative to passthrough, so this should also work for your Cubox.
As for why you can't bitstream DTS-HD from the Cubox, maybe you should ask on a Cubox support forum.
As for why you can't bitstream DTS-HD from the Cubox, maybe you should ask on a Cubox support forum.