damn, i worked alot to find this, probably most of you know it but none of the posts in this forum helped me, so i thought there might be others like i am.
okay here it is:
1-make your character and save it:p
1,5-always work from the front view
2-make a biped to fit into your character, but dont apply physic modifier, and dont forget to keep the bone sizes as 3/4 of the size of your character(so later on envelopes will fit better)
3-delete the character from scene and leave the biped only.
4-export the biped as filmbox(*.fbx)
5-reset max
6-open your character
7-import the filmbox file into the scene with default values, now you should see bones perfectly fit into your character.
8-apply skin modifier to character and add all the bones to it, if you paid attention to 3/4 size of the biped you wont have to deal with envelopes now.
9-get panda x exporter and use following options to export your x file
it should work, it has to, works for me