So I found the DT770 to be too bassy and it felt bloated. I also found they had a distinct lack of midrange, so basically a lot of bass and top end but nothing much in the middle.
They are very comfortable and as you probably well know, bomb proof and whilst the AKG's are also very well made, they do need a good fit round the ears to get the best sound and therefore are a bit picky with placement.
But for closed back they do sound spacious and I think quite natural, nothing is emphasised. Vocals sound really good.
Agree the Dt 770 is lacking in the mid range.. I fine leatherette to get sweaty though...puts be off the AKG 550 s