Welcome to AO.
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.
Hope it helps.