I believe the head shells for the 312 and the 312S are identical both made from Magnesium. When you refer to material used the arm tube of the 312 is made form Aluminum the 312S is made form Magnesium. Internal wiring in the 312S different from the one used in the 312 - better ? - no different.
Which ever one sounds best to you is the best one for you
Good Listening
Peter
Which ever one sounds best to you is the best one for you
Good Listening
Peter