stereo upgrade

I have the monsoon setup with my 04 GP. Im looking to upgrade the speakers and maybe add small sub (10inch) input as to what will sound best in the doors and also find out if replacing the 6x9's and leaving the factory amp to run the new 6x9's is worth doing? I'm not fooling with the head unit (don't want probs with onstar and computer) and like the indash 6 disk setup. Need some suggstings please. Also, does anyone really know how clean the factory amp is in the trunk and what power it puts out? Thanks to all for input.

I was wondering if i could get some input on replacing my factory cd player in my 2004 gt1 like how do i get it out and to the back of it.