It would be two DRSSTC (Dual Resident Solid State Tesla Coil) units which are MIDI controlled. There's a fiber optic cable running to some digital logic boards that are in the Tesla coils.
The Open Labs MiKO MIDI console hosts the PC Software (Fruity Loops) that they use to actually sequence the music.
The MiKO is just a Windows machine with a bunch of nice MIDI interfaces, cased in metal—which is nice because they have a lot of EMF emitted from the coils. It used to actually run off a laptop, but it would crash all the time.
The drum machine has a solenoid for every drum, and they're MIDI controlled also...from the MiKO.
There are a few ways that you can audio modulate a Tesla coil—this way is known as PRM modulation or pulse rate modulation.