Marty,
I created a lash up in Legacy with a BB as leading engine and a SP crew talk caboose at the end;BB in Legacy mode, caboose has Train Sound with TMCC and has an ENG-id, however as command type in Info mode ACC.
When applying Train link in the lash up, the caboose will appear with ENG, and symbols for track and and water tower(considering ACC) on the remote Screen. .
In this case crew talk of the BB and crew talk of the caboose via Train link are Independent and do not interfere.
In case ACC would be replaced by ENG in Info mode, the caboose would be silent in Train link.
Maybe that is a work around.
Albrecht