seat out job I am afraid. if your seats don't fold you won;t get the parcel shelf out in one peice.
seats backs are held in from the boot side IIRC, should be relatively simple to loosen them and push them forward whilst you pop up the shelf
so instead of using a nice rubber grommet thats already provided for you in the ECU Box, you'd rather drill a hole thru the car body?!
ECU box is the safest route inside the car.
i think the big square thingy is suppose to be an amp or something. but i'm sure someone will correct me soon.
the amp is fed line level from the little extra block on the back of the head unit.
Concert only amplifies the front channels itself, or none in a bose setup.