There is good news for REFERENCE 600 owners. The same sonic improvements found in the new REF300 can be obtained in a Mark II Factory Update program for the REF600. Original REF600 units are literally taken apart and painstakingly rebuilt with new output circuit boards and new input / regulator board, using all-new components. The rear panel is also retrofitted with a new three-pin, 20-amp A.C. connector and detachable cord.