I've transported an Avant 32 over a distance of 60-odd miles in the back of my E-class - the hydraulic suspension will help a bit, and it'll fit with no problems (as long as it's not in its original packaging, I suspect that'd be a bit tight). If you can, take a few duvets / pillows / WHY to stuff under the middle. Avoid putting any weight on the speaker fret panel. Try to put a bit more under the screen frame as it doesn't quite lie flat with the base circle still on.
And I might add, this is not my current Avant - I transported this one upright and now the tube is going! Maybe a long lie down is good for them 😁 (although I doubt it)
I might add, the other day I had a wardrobe in the back of my E-class... over 6' x about 4'.... I nearly haemorrhaged when I remembered the electric closer, just in time to watch it pull the rear window glass to within about 2mm of the corner of the wardrobe....😮
Speaking of which, if anyone needs a hand moving B&o bits, just yell - I'm in South London / Surrey and don't mind mucking in for a fellow lunatic.