That's a very similar problem to the one in Neal Stephenson's 'Diamond Age'; the Primer that drives the story is narrated by paid 'ractors', but later the book is copied and mass-produced, and paying for all of those to be acted would be prohibitively expensive; so the voice parts are replaced by simpler, synthetic voices.

Me, I always thought the way this tech would pan out would be as voice-changing; you capture the actor's voice you want, then the writer speaks the lines and the computer restyles them as an imitation of the actor - this seemed a more natural way to input emotion and pacing.