I bought a set of small moving lights off Ebay and did this to my Kiss Pro over 4 years ago. Lights were about $70 each.
I only needed to add a DMX link cable between the two. Set one to master and the other to slave. All sound activated. I even set the slave to mirror the master so they both didn't do *exactly* the same thing all the time.
The only problem is that these things are on ALL THE TIME. So yes, it does get annoying/distracting after a while. Now if they were somehow tied to the game logic and only activated during certain modes of the game, THAT would be a great mod.