FWIW, I searched and discovered that if you simply hook up an LED to the pos/neg wire to your subs they will flash to the beat.

I didnt know this was so, I took an old LED map light and holder/base and connected it and danged if it didnt flash

My amp has the ability to set the display in several colors so now Im wondering what color LED to use. My map lights are green so maybe greeen Of course I imagine flashing blue back there would really intrigue the cops but maybe my tint will keep it from being so visible.