2003 Silverado Amp Install?

I have a 2003 silverado with the in dash 6 disk changer, bose sound system, no on-star.  I am wanting to add a 10" boston sub and and xtant 300 watt amplifier.  I originally just got my signal for the amp from the speakers at the rear doors, until i realized that there was an amplifier independent of the deck.  My question now is how should i hook it all up to get the best sound out of it.  I have seen that PAC makes some products that seems like they would work.  But how would this be any different that just tapping the wires from the deck into the amp to get my signal.  Any help would be greatly appreciated.

Thanks alot!

You wont really get the great sound out of a subwoofer with a factory radio. A good choice would be to change the factory radio and get one with an independent subwoofer output.

A decent radio will give you better control over your other speakers and will be more powerful than your factory unit.