Doug,
You need to confirm with the customer if its a wax based product or an acrylic. There are a few products out there called "wax" but are in fact acrylic sealer.
Assuming it is wax then a good stripping back will be necessary and then you can apply a topical sealer. If it is natural stone then a breathable product is desirable. This is assuming the customer wants a sheen on the tiles. It may be possible to polish the tiles themselves and then apply a colour enhancing impregnator. This would always be my preferred option if practical.
Be careful with the pressure on your spinner as softer stones can be damaged with a spinner.
Do you know what type of stone they are or have a picture?