My Beo4 manual (part number 3501025? printed 0405?) says ...
NOTE! "Buttons" marked with a * apply only to previous versions of the Beo4 remote control.
... and then ...
CD2* (compact disc player 2) For switching on a second CD player in certain Bang & Olufsen audio systems.
... so it seems that this is not for ...
McRib: some future option for the master system
... but I am not sure for which system it was designed !
First B&O (1976) was a Beogram 1500 ... latest (2011) change has been to couple the BL11 with the BL6Ks *sounds superb*