I have a 94 Dodge Ram van with an Infinity stereo and each of the 4 speakers have their own built in power amplifier. You cannot just change the speakers because the amp is not at the main unit. Your setup may be different though so check one of your speakers first to see how it's set up.
Thanks Jim. My speakers don't have the amps on them. That, as far as I know, is Infinity only. My truck didn't originally come with the Infinity system.