I've just uploaded an online chapter (with code) on program sonification -- that's the conversion of an executing program into audio. I've used a mix of spoken words, MIDI note generation, and audio clips.
Part of the application includes an explanation of how to get FreeTTS up and running, and how to add three US voices from the MBROLA site.
The FreeTTS code is quite separate from the rest of the sonification application, and includes two simple examples -- code to list all installed voices, and code to say a sentence input by the user.
The online chapter is at my Killer Game Programming in Java website:
It's chapter "Java Art Chapter 5. Program Sonification", located about half way down the page.