Kim uses PCM, which I believe has been generated offline by a rather nice TTS.

If you want to run TTS on the player, you might consider Flite (http://www.speech.cs.cmu.edu/flite/) which is rather more managable than Festival. The quality isn't bad for a free system - but not a patch on the commercial ones. It has been observed to run successfully on an ARM Linux platform not so dissimilar to the car player.

Rob