you need to remove the fasteners in those little pockets next to where it says "accessory ready" the front part of the grill piece is trapped underneath that plastic.
there likely is not wiring to support the B&O if you didnt get it from the factory. further the head unit wont be configured to work with the B&O if you didnt get it with B&O originally. lastly the rear quarter trim is different if you have the sub so that would need to be modified too.
A...
some others reported that some of the fasteners in that area could use a few more turns (behind that trim panel). that would be my first place to look as it is closest to the sub
i would be careful with stuffing the box with poly fill as it is a ported box. increasing the effective volume of the internal volume will lower the resonant point of the port. Depending on the EQ done, it may make it sound worse.
blast some 40hz test tones and go stand buy the subwoofer. it should be fairly obvious at that point if its playing or not. worst case scenario, pop off the rear panel in watch the woofer. if should be moving like crazy.
the EQ settings have a bass adjustment you can use to alter the frequency response. but the subwoofer will be playing a low frequency. it's much harder to tell where a low frequency is coming from.
there is some typos in the graphic for the B&o system.
the front LH & RH speakers are 100mm with a 25mm tweeter on top. there is also an amp on top of the subwoofer that is omitted. (Probably already mentioned)
i've seen various questions about what signal the rear pods receive. in all the...
someone posted a wiring diagram around here before i think
The amp powers the front RH & LH sets of speakers and the DVC (6 channels)
the other speakers are powered by the head unit