The KB Rejectostat system had the capability of being used to supply multiple receivers.
In the diagram above KB advocate using something like 3 pin mains sockets to act as aerial sockets to plug in a single radio into multiple rooms, or to plug in multiple radios onto the aerial distribution system. A matching 3 pin plug would be inserted into each socket on the distribution system and that would be connected to the radio rejectostat unit with screened cable then into the aerial and earth sockets of the radio
KB had the contract for the supply of radio apparatus to the 3 liners Queen Mary, Queen Elizabeth, and the Caronia.
I cant be sure but they may have used the Rejectostat system for the aerial distribution. Or they may have used a system of "piped" radio stations on a 100v line speaker distribution system with a station selection switch, I am not sure.
Some of the advertising posters can be seen here.
http://www.kbmuseum.org.uk/kb_posters.htm
Together with a copy of the souvenir brochure for the Queen Mary. Which I bought in the hope it might give an in-site to the radio systems, but it didn't.
Mike