Update: Final Fantasy XIII's composer Masashi Hamauzu was presenting the live event. He didn't say much but has said the main theme doesn't have a title yet and probably won't until the game is completed. He also had a 5 minute "interview" talking about the process of composing a song. That's all we have so far.
According to http://ff13.xrea.jp/, the Live Premiere Final Fantasy XIII event that was taking place today only lasted 20 minutes and included the trailers without voices.
The event lasted 25 minutes less than it was supposed to and included no new announcements from Square-Enix. They did preview two new tracks including the main theme though.
Sadly, that was the main point of the show...it was a live music event. We'll update you as we get more info. More PlayStation 3 News...