just cut off the plugs for the speakers and you can fit anything you want ,i have made some boxes fitted to the ply lining on top of the wheel arches to take a pair of 6x9 mutant speakers that are a great price from a1 motor stores and sound good enough for me
will change the door speaker at some stage .. i also fitted the power socket to the wheel arch box towards the back door
will take some pics when speakers are fitted should arrive today