Congrats on what is evidently a stunning car, but one minor point I would have to disagree on - the Burmeister system is possibly one of the worst 'Premium' systems i've heard in a car of this ilk. I was supremely disappointed by it - I would have thought it was even worse in a convertible?!
I have to say, audio is one area Mercedes seriously dropped the ball on with the C63...
I was discussing this with Mark at Comand Online recently as there's a long running thread on PH about people disappointed with various factory fit "premium" Burmeister/HK type systems.
He reckons half the time you're literally paying the amp and the amp alone; the manufacture often fits standard paper cone speakers(!).
They sell Morel door speakers & tweeters and various subs. I just had a 10 inch 150 watt (I think) sub fitted behind a boot panel which has made a big difference to my (non-premium) set up. Next, I'm going to get some Morels to replace the front door speakers & tweeters. Plus some Dynamat on the door skins. Under £1k all in.