Anyone know of a switch I can install to kill the power to my amp driving my sub? It would be good to be able to toggle off the boom when the family is in the car.....

 

Your amp (the Alpine MRP 650, right?) has a remote turn-on lead to turn the amp on and off. It's a low-current, 12V connection, so you would just need to put an inline switch into the remote wire leading to the amp.

Now, depending on what you're using for crossovers and where you have the crossover frequency set, this might leave you without any bass at all, but it will accomplish what you're wanting to do (turning off the amp).