If they are just for yourself, then why not forget about MAT poses altogether and use the better material collections (.mc6)? You can save them from the material room (as you got Poser 6)... And if for some funky reason you really want MAT poses with all their flaws then open an existing MAT pose file in a text editor and compare it with the material collection you created in the material room in the same text editor. It should be very easy to find out which parts of the material collection to replace with what part of the MAT pose file.