I don't know, solubilities sometimes don't matter because of Lechatlier's principle which basically is that even if its acid pH and not technically very soluble, some small amount does dissolve and when it does it drives the equilibrium to replenish that which was consumed by dissolving, and the body usually works best on small amounts of things, provided over time. but I do know that the 6 contains the same proportion of the minerals that are present in the hydroxyapatite of the teeth, which is very convenient when chewing on bran for remineralization regardless of pH of the spit. using the 6 probably would speed things up from a concentration standpoint provided the other necessary enzymes and osteoblasts are present. that means uninhibited by fluorides, mercury, etc.