Don... I've seen this video and others several times, and I don't think the "playing" is legit. If you look carefully at where the balls are landing on the keys versus the notes that are being played you will see that there is very little correlation.

My guess is that he has the notes in the song programmed into the synthesizer and that every time a ball hits the keypad it plays the next note.

Still a pretty impressive display of juggling. I know I'd get about 2 notes played before I dropped all the balls.