I am using two SONY DVP-CX995V changers with an MX-3000. The Power ON and Power OFF discrete codes are available in the MX-3000 database. I can confirm that these ARE discrete codes and that they are distinct for the two code sets. The third code set is also present in the database. I have not tested it yet, but I'd be surprised if it was a duplicate of CM-2. Are you sure the database for the 850 does not contain these code sets?