It would have to be the platter/bearing. Sonically this would give you the biggest improvement as the newer inverted bearing/acrylic platter is a big jump over the old bearing. Moreover, it has a provision to further upgrade by way of the outer ring which will improve your sonics to another level. While at it change to the HR-X record weight with the ring. The SDS is essential but I would put it last. It will not give you the same sonic improvement the platter/bearing and outer ring/HR-X record weight would.
