A computer that runs a DMX system does not have to be a PC or have internet. DMX systems started to be used in the mid-late 80s. Before then Microplex systems were used to do theatrical dimming. DMX is not some crazy new technology that wasn't available when Indy was built. The computers that run the EMVs are far more than capable to run a DMX sequence for flickering lights.
I'm not saying that this is how it's done in Indy. But it's how I would have done it. An analog system would be almost just as complicated if you wanted it to match the sounds with the generator.