From what I've gathered.....
Super Pas = looks like a Dynaco Pas, with new parts on existing Dynaco circuit boards, and modified power supply with no board.
Super Pas 2 = built on a Dynaco chassis, with new power supply board, and 2 new circuit boards, same circuit as the Super Pas, just on redesigned new boards. Silver front panel or black panel. Optional buffer boards were available for line/phono.
Super Pas 3 = Identical to the Super Pas 2, but with new chassis and knobs, looks totally different, but sound identical to the Super Pas 2.
Super Pas 4 = Super Pas 3 + buffer circuit on the same board.
Therefore, a Super Pas 4 sounds exactly like a Super Pas 2 with the buffer circuits for line/phono.