Saltillo is supposed to look glossy, and I'm not sure if you can get a non-glossy surface if they are sealed properly. "Wax" for saltillo tiles is actually an acrylic coating. It is especially important that you have a good sealed and polish surface outdoors to repel dirt and rain. If you don't, I can guarentee that the tiles will look heavily soiled in time. Saltillo is very permeable which makes them absorb water and dirt. Saltillo is very hard to clean once this happens.
Do a search for saltillo polish on the web, and perhaps you will find a low gloss formula, but be sure to keep them sealed.