I have some of those lightning FX boxes and know color organs and such all make lights turn on/get brighter with sound. Is there a simple way to do it the opposite, so when the sound gets louder the lights get less bright?
Well, anything that increases can be inverted. And any microcontroller like an Arduino can take a sensor and use it to control relays or a circuit that varies voltage to a device. But both these options require time and materials. Are you looking for something out of the box? Maybe Light O Rama has something?