After a lot of research, I have just found out that although both are 75mm burrs (Atom & Mythos) they are different in cut and design and part number. Because of the costs involved I will not be buying an Atom 75W now. Instead I will look for a used Zenith or Olympus 75 and swop the burrs over. So, if anyone has one gathering dust, I can offer it a good home!