I have the B&W premium sound system in my 2011. I'm not that impressed with the system. First step is to reinforce the mid to sub frequency with an aftermarket 10" sub.

We can't get a preamp analog signal because there isn't one, the digital MOST system for data goes to the stock amp. We have to take the processed speaker level feed from the amp and use an aftermarket amp that can accept this high level input.

There are two negative - and two positive + connections from the amp as the single speaker in the sub is a dual voice coil.

I bought the TOPlx wiring diagram so here is the sub wiring



You can take this from the amp or from the connection at the sub.

I'll post a picture when I actually have things mounted up.

 

I'm looking forward to seeing your setup and results. The B&W system in the XFR leaves me feeling empty compared to the Meridian system in my Evoque.