Dual trigger system

You can probably do it with just a switch.  The easy way would be to do a current draw on the radio's acc wire.  The problem with doing it this way is that the voltage will backfeed and power more then just the radio, so you need to know how much current you'll need to energize this circuit.  Once you know the current then you can get the appropriately rated switch.

The 'right' way to do it would be to wire a relay in to the accessory wire on the radio (the red wire).  Wire pin 30 to the radio side, wire 87A to the car side of the red wire, and wire pins 86 and 87 to a fused 12vdc source.  Wire pin 85 through your switch to ground.  Now, when you hit the switch the relay will energize and turn your radio on, and the radio will turn your amps on.

Now, you can look forward to dead batteries when you forget to shut it off!!!  :)

Well, the first way I described will backfeed, as you arn't actually isolating anything.

The second way, with a relay, will isolate your radio power supply from the car, therefore, it won't backfeed, which won't allow it to power anything else.