Anyone would have any tips on making this workflow work?

It seems that it just need the rig to fit both ways, because with the Import Exclusive Merge when in Max can import the animation without problem. I think the issue is how to characterize the CS-Biped hierarchy in Motion Builder. There are some strange things when doing that. For example, CS-Biped shoulders are parented to the Bip NECK, not the latest spine, and Motion Builder does not accept that hierarchy. So, in MB, when you move the neck you move together the shoulders and arms. Which is not that big of an issue because the neck could later be animated on Max. The biggest problem is with the Bip01 Pelvis, which when imported into MB function more like a Root than the Pelvis because its only child is the Spine1, and the legs are parented to the Spine1, not the Pelvis.

One possible solution to both problems would be to simply unparent the legs from the Spine and parent them to the Pelvis, and unparent the shoulders from the Neck and parent to the latest Spine, but I haven’t had time to test it throughly. Would a changed Biped in Motion Builder import correctly in Max later on?

eks
PS: Btw, I forgot to add, my goal is to use Biped skeleton (for compatibility) to animate in Motion Builder, then later import this animation over Biped to export.

This is why you should google something before posting already answered questions in forums.