I've expermented with this there are 2 ways to do it.
1. Goto radio shack and buy a power inverter, you need at least 5 amps, these are expensive.
Or you can do what I did. Go to a used computer/parts dealer and buy an AT computer power supply, Usually there is a stick on top that says how many volts each wire is. All you have to do is look at the end of one of the 4 pin molex connectors (little plastic thing with wires in it). Cut it off and look at the stick to find the 12v wire strip that and a ground wire. To hook it up to an amp just run the ground wire to the ground, and the 12v to the 12v, for the remote just run a 12v wire to it. Make sure to get an AT power supply because they operate with a button, ATX rely on the computer motherboard to turn it off so if you had one when ever you wanted to turn everything off you would have to unplug it... Hope that was helpful