I use both Brian and Kate and setup a command to switch between them and a few other voices I have.
Me: May please speak with ...Jarvis
VC: Sure just a moment while I get him.
Invoke SelectTTS voice by number (or you can use by name) to select Brian
VC: Hello, this is. Jarvis, how may I help you?
When I get tired of talking to one I just ask to speak to another. Works great and gives a little variety. My computer has multiple personalities.