I had a tiny bit of progress with the subwoofer problem today.
After getting that curt initial response from B&O, I sent them a further email questioning whether they really were happy to wash their hands of the problem or whether they may see it appropriate to escalate this through to AMG HQ on my behalf. Their response at this point was spot on and this appears to have kickstarted them into action.
B&O's AMG development guy got in touch with his contact at AMG in Affalterbach and I got a response asking me to get my dealer to contact a specific person at the factory 'before they start dismantling the car to remove the sub'. I think they know something!....and it ain't something that needs a new sub to fix it.
Dealer and factory are now in contact and lets see how this develops. I may get it fixed yet
It would have been easy to give up after that first response but, well, that just isn't my style.