Hi Norman,
Yes, this is possible. Do your Penta speakers have 2 x 8 pin Powerlink sockets fitted please? If so then please let me know as a different cable can be used, otherwise please use the cable in the link above.
Please connect the Pentas to the Beosystem 4 using one of the RJ45 Powerlink outputs, then you can link the Beomaster RCA Tape outputs to the Beosystem to share the speakers via this cable:-
Location: The cable workshop, England
My B&O Icons: