Text To Speech: Siri Voice Won't Work?

I'm trying to have the new iOS 11 Siri voice be my new text-to-speech assistant, but selecting her voice in the Speech Interface (General––Accessibility––Speech––Voices) doesn't activate the voice itself. It instead uses the "Samantha" voice which seems to be the original Siri voice pattern. Yet when I select another voice (Samantha Enhanced) it does activate.

Is there a way to actually select Siri's voice?