I've actually tried this myself, by following the instructions Phil posted
here. Unfortunately,
something about it reduced the on-screen text to just "M". Same in my own game. I might be doing something wrong myself, but you're just missing a bunch of steps.
The default framework, the template as it were, that Sierra used is all set up to play audio (where available) for any message spoken by the
Narrator or any
Talker, depending on the value of
gMessageType/
global90. So yes,
it would know.Oh, also? There are parts that would
not. The intro, for example, when Roger dictates a log and it appears word-for-word? That uses messages as a source, but neither
Narrator nor anything derived from it, so that wouldn't be automatically voiced.