Add this to the above questions.
Looking back, I think a little clarification in activating Horn Master is needed.
1/ The firmware must be version 9-3-2 (in one of the Diesel loco sound sets)
2/ Enable "Only Supported CVs"
3/ _ _ _ _ _ _ _ ?
What else is needed in order to enable Horn Master?
Is there a steam version of Horn Master? If so, what is required to enable it?
Thanks again for your help.