Modifying existing animations?

The animation format is gr2, but ma and mb are the source files, which are unavailable.

Hmm, that seems a bit strange... gr2 contains both the skeleton and the animations. The problem is that the animations don't play in 3ds Max. I just checked this with one animation, renamed the file format from ma to gr2, and it was imported into Max. The problem is that I don't see how to edit it. The animation doesn't play, as far as I can tell, although the skeleton's position corresponds to the beginning of the animation.

In any case, mb files do exist, and I was able to export the models without any particular problems, even open them.