PC Magazine has a feature on Infinity Visions whose software coordinates the largest pyrotechnic shows. "The software allows firing cues to be placed at certain times, superimposed against the waveform of the music that will be played; fireworks can be used to emphasize themes, provide percussion, or simply create effects that complement the music. Once the show is choreographed, the instructional files are uploaded into the firing machines, and the programmers can step back and simply push "play". The computer sends the appropriate signals down a web of cables to the firing modules, which in turn are connected to the shells."
Above is the better of some 70 fireworks shots I did yesterday. Boston's show was choreographed with Infinity Vision's product.