Not sure if this has been posted already...
Buy sheets of dry ice and place them on the individual tiles. Wait about five or more minutes. Smack them with a mallet. If they are cold enough, they will pop off cleanly and sometimes in one piece. I've done this with tile set directly on plywood and it takes up the tile AND grout completely. But it makes it hard to throw away the many whole tiles you will get up with this method.
Start with 50 pounds and keep leap-frogging the pieces as you move to the next tile. I've found having 3-4 rows of dry ice ahead of the tile you're working on allows you to keep going without needing to give the ice more time to freeze the tile.
In the attached pic I had started with 10 pounds. You can see what's left. Most of the tiles came up in one piece. I ended up going back for another 40 pounds to finish the job.