By the time you put wonderboard, mud and tiles or stone on your treads, your first step will be 1"+ too high and your top step will be 1"+ too low. Your tread heights are a critical consideration. Also, I know a lot of guys swear by the wonderboard, but I think it is a real pain to work with and that it is no better than plywood. Mel is totally right when he points to the real problem being the condition of your existing stairway. There is movement in the wood stairway that is causing the tiles to crack. In older houses it is usually not practical to even attempt to stablilize a stairway well enough to put tile on it. You could even build a whole new stairway and it would still get screwed up if the floor it was on was bouncy or the second floor was, or if the house swayed a little in the wind (which is common). The stair fram and the finish risers and treads probably ALL need attention. What you want to do is really not that practical. I think your best bet is to have the stairs sanded down, patched up and re-glued and fastened, etc. by a finish carpenter, and then have someone come in and put a faux finish on the stairs. Someone could easily do a marbleized finish to simulate any kind of stone you like. You could then put several coats of a very hard, crystal clear (not amber) finish with some sort of urathane or something.