I added a 10" sub behind the rear seat of my '25 Mav that doesn't have the B&O System. These Mavericks have bass frequencies trimmed out of the signal to the rear speakers, which don't make them good candidates to tap off of for a sub.
The flat eq mentioned in the post you referenced fixes that...
I've got a drop in rubber mat, but honestly it completely sucks for my use case. I slide a lot of heavy stuff in and out of the bed of my mav and the one I have now has a tendency to bunch up at the back of the bed.
2025 XLT AWD Hybrid