Re the head unit, if you have removed all the surrounding bits make sure you have also removed the trim piece that sit flush with the head unit.
-Once this trim is removed, part of the head unit will be exposed on the sides.
-If you look halfway up on the side of the head unit you will see a cutout that sits at slight angle.
-Insert a screwdriver in the cut outs on both side to disengae the retaining clips
-Pushing the screwdrivers in wiggle the head unit till it starts to come out.