How were you able to mount the speakers if you broke the screw tabs off the speakers? The guy on crutch told me to use the factory brackets but it appears the speakers and factory bracket are one piece.
My Infinity speakers had the four mounting holes that lined up with the door panel mounting holes... but also had four "extra" mounting tabs for some reason. They would not sit flush in the 6x8 opening with those tabs.
I looked at a picture of your new speakers and it appears they also have "extra tabs" protruding out of them on the long sides. JL Audio C2-570X - Yahoo Image Search Results
I don't want to make a wrong assumption since I don't have a Shaker system, but I would guess those two tabs are preventing you from getting them in flush.