does anyone know if 6X9s will fit in the doors of a 06 crewcab duramax

Nope, 6's or 6 1/2's.
John

6.5" or smaller will fit without modification. Anything larger than 6.5" will require serious fabrication and reconstruction of the door.

Can't see why anyone would want 6x9's anyways.

My 06 crewcab has 6.5 in the front which pop right out. The rear are 5.25, I am thinking about replacing them so I just took a front and rear door panel off. Some say 6.5 in the rear but any good speaker would be too deep and thats why it has a spacer.