Some info on Reatek (RTD*) based players.
These players runs linux applications, but only if they are compiled for mips/mipsel arch, try google for more info.
I don't know much about MiniMyth, but i suppose it is a standard linux arch, such as x86 or x86_64, so this isn't compatible with RTD players.
The source code APACER released you're referring to, is only for the core apps within system, such as kernel, services and so on.
However most important application on these players is "DvdPlayer" app. which is developed by Realtek it is NOT opensource.
DvdPlayer application handles everything you see on the screen (menus, playback...). Further, it is using custom Realtek video/audio decoding chipset for media playback.
This Realtek decoder chipset is not as same as standard GPU cards, so again, this also isn't supported by MiniMyth.