I might or might not expand on this later. But for now I will give some of my opinions on the AKG K553 Pro Studio headphones.
I got mine last Friday (24th/April), the delivery took a while with the freight forwarder to Europe. So keep that in mind if you are ordering this time on Massdrop. By the way they are back up as of 27th march in limited numbers (627 available, 1800 were sold last time round).
I really like the sound these make. It is very accurate sound leaning toward anynitical. It is very nice to listen to well produced, well spaced music on, but it shows up flaws, distortions and flat sound pretty quickly.
The bass is something they were supposed to have improved over the K550's but I have never owned or heard them so I cannot comment on that. What I can say is the bass is present and clearly defined, it is not loud and will not interfere with the other sounds at all.
The noise isolation is not wonderful, but they are Pro Studio headphones so I gather they were aimed at use in a quiet isolated studio anyway. I bought these for use with my PC as half of a better headset. For this they really shine as the room is quiet, it isolates from the fan sounds on my PC just fine and the sound as above is very good indeed. They do have a wide soundstage so use in games is also very nice.
I would not recommend getting these if you want an everyday carry, city use headphone. With the not wonderful isolation this have car, train and people noise will get in pretty readily. Again these are supposed to be studio headphones so this does not bother me at all.
They are very comfortable, the ear cushions surround your ear and are very soft, the headband is flat and cushioned but with firmer foam. The headband is just a band or metal, fine for non abusive use but I would not throw these in and out of a work bag every day, again not aimed at that so this is fine. It also has a three meter long (9ft),cable, non detachable, and the cable is good heavy thick cable not braided.
I really very much like these headphones.
Compared to my California Headphone Company Silverados, the K553's are not as good a seal on the head, have much lower clamping force (very light in fact), lighter over all (silverados are all metal), but they have a much more accurate sound (silverados are bass heavy). So with these I have my set of everyday carry headphones to abuse (CHCs) and my home use delicate headphones.
Any questions ask away, I am just not a real audiophile so answers may vary.