Neither mix should be used. Filling cavities went out of practice in the '30s. Alex Shigo has shared a lot of information about how trees compartmentalize decay to keep it in the old wood.

About the only thing that you can do for the tree is to bust out any of the loose chunks of rotten wood. Do this only if you can without damaging any solid wood.

doing anything to increase the health of the tree makes the most sense. If it is in a natural wooded setting you could skip mulching. If not, mulch with about a 5" _layer_ of coarse chips, preferably from the same species. Keep the mulch ring away from the trunk, think donut not volcano. Water if you can.