The archduke was trying to communicate with her, but his telepathy seemed to be one-sided. If anything, the only downside of this system's ability to hear the Whispers of the Heart was that she couldn't communicate back to the people through her mind. It was not like the system was too weak to grant her telepathy, but it was more like it wasn't letting her learn telepathy. Her only telepathy skill was a steed ability.
She didn't know when Larkin was able to have this passive skill, but it was probably one of the things that he had gained from the power coming from the Gates. As for Herriot's voice, that was a whisper. Then again, none of the two probably knew that Artie had received their messages.