ar.01 files, imported the models into 3DS max 2013 (which was difficult to find), and converted the hkx animations into. I've, so far, extracted the data from the CPK, extracted the data from the Classic Sonics. I've been following the info on this page (Bottom of the first post).
Anyway, enough about what I've been going through to try and find this information.
Everywhere I look, it seems that its either a dead end, or I get told that it just can't be done (Despite me seeing lots of videos that proves that its been done). I have spent about 2 weeks trying to figure this out.