Well not sure how I can help since the way that Softimage does it is a bit different, I've never seen branch selection options in 3ds max but it's been a long time since I've used it. In Softimage when you export a dotXSI file for JA you want to branch select model_root, now if you notice old 3ds max tutorials show that being named as B:model_root, the "B:" standing for "branch select" in SI code. The main benefit to having an export selected function is only exporting what you want and not other parts of the scene, like say if you watch my character animation tutorial video for instance. Both the rig and the JA skeleton with mesh are under the same node but since I only branch select model_root everything else is ignored. For this sort of thing you might also want a plot animations feature, it's nice not having to keyframe all the bones before export.