MotionBuilder will not work since the 3dx rig cannot be validated in it .. the 3dx rig uses custom bone names. It's easier to just export bvh from another program.   I am working on a Blender rig for that .. (blender export to bvh -> max import to bvh -> max convert to bip). So far I have gotten everything right except for hand movements, the neck, and one of the spine bones. Once I get those right I can focus on the remaining less-important bones. It'll just take some trial and error si