Yeah. You need to remove the trim underneath the boot lip, this allows you to remove the side panel. The side panel in the boot is held in place by the 2 cargo brackets, one plastic screw up behind the rear lights, and one screw hidden behind the rear speaker panel. This is the one screw you can't get to without either removing the rear speaker panel, or at least pulling the panel away from the bodywork where it meets the boot panel. The screw is up near the seat belt spool. It is a bit of a pain. If you're selling the subwoofer, I'm interested, or you can upgrade it with some minor DIY, let me know?
Cheers, Andy