There's still plenty of time for it all to come to nothing.
Which it did, sadly.
I had two follow-up calls from the same helpful chap at Audi customer services, as promised, but he didn't have any good news.
According to Audi, my car - and others similarly equipped and built around the same time, give or take - have a version of the MMI firmware which there is no intention of providing an update for.
Period.
We've fallen through a crack, I'm afraid.
I'm going to throw the towel in at this point.
Notwithstanding the fact that the subwoofer control should be there - the manual says so, apart from anything else - I simply wouldn't be making enough use of it to justify spending any more time trying to get it. And although its absence will continue to niggle at me, life's too short.
That doesn't stop me thinking that it's a pretty poor show all round, but you win some and you lose some.
Irritating, but not the end of the world.
I've absolutely no reason to suspect that I was being fobbed off in my conversations with the bloke at Audi. None whatsoever. He and I talked about this for the best part of an hour over the course of the calls. He wouldn't have bothered with all that if he hadn't been trying as hard as he could to get to the bottom of it himself.
If someone else here is willing to take up the cudgels on behalf of the dozens - and there must be dozens and dozens - of other people in this situation, then that'd be great, and I wish you luck.
DJAlix did mention that he would try to fix this himself if he manages to access a donor car to experiment on, and I wish him luck too.
In the meantime I'm resigned to throwing away my Hardcore Rubble and Soil CDs (the ones with the bangin' bass, at least) and living on a diet of Desert Island Discs and Woman's Hour instead.
.
.