need help with monsoon 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.

Well as long that the Ohms of the ones being installed are the same as the OEM there would be no problem. And the only reason replacing the OEM I could think of is that the diaphragm is made of something more resistant to high volumes than corrugated carton. About the amp, as long as you set it up to get the power direct from battery and you drive the sub with signal from the low freq leads of the rear speakers you should be ok.