To restore these tiles you are best seeking the advice of a professional. I had a similar problem and got help from a guy in waterford. He used special machines to strip and grind the floor back and then used a special powder to repolish the tiles I think it was called crystallisation. I tried every thing myself first and purchased numerous products from tile shops, even my origional tiler did not know how to help. Any polish you put on yourself will only last days .My tiles look better now than when they were first laid. His number was 086 820 6418 ( Marble Solutions).
Good Luck