I have encoded Avatar with the BD3D2MKV3D tool, in full width 1080p SBS, h264. I have chosen "Bluray SUP" as the subtitle format.
The subtitles appear properly in MPC-HC and in the Occulus Quest native video player; by properly I mean they look very much like in the bluray on a hardware player and a TV.

In Skybox VR, the subtitles are:
- Blue instead of yellow
- Much bigger than expected
- It seems that the antialiasing is incorrect, edges are aliased.

Thanks for fixing! Besides this, that's an awesome player!