I called a bang and olufsen retailer in Germany and they were really helpful and it is simpler than thought.
A buy a rcd to 3.5 mm cable
B connect rca end to l/r pre-amp out
C if beolab 28’s are linked, determine which one is the predominant one
D connect 3.5 mm business end to the predominant 28 which when in use will wirelessly connect with the slave 28.
and that’s all there is to it lol!
