I got the voice guidance working with marble and marble maps latest versions (1.1.1) and monav (0.3). I used the Tomtom estonian voice.
But as this is more a technology preview I guess that it is not ready yet
I have made some tests during last 2 weeks and most of the "commands" were wrong (sounded in wrong places) or at least confusing. Tried to understand if there is some systematic error or shift in them, but until now I have no idea....