So... They used Unity3D (LOL, sic!).
FMVXYZ.bytes files are pure OGG
mbgXYZ.bytes files are also pure OGG
P0dataXYZ.bin are "Unity Web Player Scene (non compressed)":
Open with UnityEx 1.5
sharedassets files, open with UnityEx 1.5
By the way> This can help in reversing FF8 (and FF7 if there's something missing). The engine is similar, so...
So far the most interesting source files are (for related FF):
PSX_LIBGPU.cs (Contains many polygon infos, vertex etc.) [Names like TPage and etc.]
PSX_LIBGTE_EMU.cs - I've seen this huge array in FF8 pseudocode...
PSX.cs - Many definitions about colour, TIM width etc.
PsxCamera.cs - Contains debug dumper for Camera info (reverse engineering?) and ready camera class (Matrix translation etc.)
PSXTexture.cs - Generating texture from TIM? (Yeah, setting new bitmap, copying pixels according to data. Looks like TIM to Bitmap generator)