Amplifier/Sub Question

I have a question about my amp; When Circuit City originally put in my aftermarket radio, they wired the speakers to the amp, rather than the radio (at the time the truck didn't have a sub) Now that I have a sub, I can't wire the sub into the amp. Is there a way to have the sub & spakers into 1 amp? Does anyone know?

 

How many channels is the amp?

 

What kind of amp is it, how many channels, is it bridgeable? Post the amps specs and we'll see. Are your stock speakers wired to the amp? Your head unit output goes through the amp to speakers unless you only want the headunit to power speakers and the amp to only power sub.