I spent an extensive amount of time comparing the 940 and 840. I personally prefer the 940. Not because I think they're superior but because I'm not a fan of the 840's mid bass hump. As I observed before the drivers are very similar (possibly the same?) and the back of the cups are close in construction. It also looks that the both of them weren't built for acoustics. The back of the left and right cups from both headphones are vastly different from the left and right cup. It looks like it was thrown together. Search the thread for my pics and it's quite clear.
I can't wait to hear what Tyll has to say. While I may disagree with his preference, I believe Tyll's measurements will be done without bias and his assessments made from his experiences.