Oh, I wondered what that was when the road service guy replaced the wheel from a puncture! I'll check if mine is screwed in like yours - thanks for the pic
Looking in my book the 8 speaker system with sub was optional for the rs liftback only when the v6 was optioned.
I installed a amp+sub box in mine and it is very easy because the radio silverbox is in the drivers side footwell so it is 1 screw to get to the wiring to add the sub.
mine has never output music.
with mine if you put your ear to it you get no music but if you start the vehicle it makes a sound like the engine idling.