Adding another power plug to car??

It would work but you would have to unplug or power down your sat radio everytime you werent using the car long term, sat radios will create a small draw on the electrical system, about the same as a cell phone plugged in. This is assuming you are talking about using the 12v constant power wire from the amp?

Definately do not use the "turn on wire" for the amp as it is rated at low voltage around 5 volts or so but may not be enough to power on the sat radio and or could damage your radio.

My suggestion would be to pick up a dual lighter plug adapter from radio shack. It will have two female ends and one male. Just cut off one of the females and wire it into a switched 12v source at the dash somewhere.