I found the bass needs to be dropped on the E Class, only a couple of clicks, but it took all the overpowering boominess away.
The treble just adjusts from very upper mid, from what I can tell, so upping that just adds some nasty harshness, adjusting the bass is adjusting lower mid so will take away the 'muffled voices' effect.
Unless of course someone has friend the tweeters in it already!
I am in Wymondham, so if you want to pop over with it when you get it I can have a listen and see what I think, if you think there may be a problem with it.