Blair,
The only thing you need it a turn on lead for the existing amplifiers. Your new head unit should have a remote turn on wire (usually a blue one) and you need to connect that to the turn on wire for the amps, sorry I cannot recall the color.
If you use a aftermarket harness, which I highly recommend, just connect the remote wire from the radio to the power antenna wire to the harness and this should take care of things.