You said you wanted an honest appraisal of your headphones, so here are some of my honest and unadultered experiences from using the K553 Pro (sans detachable cable) for about 5 years of heavy daily use. They begin here...
https://www.head-fi.org/threads/impressions-of-akg-k553.776393/
The pleather material began to flake off the pads after only a few months of rather heavy use. And the filter rings on the baffle plate also started to come loose in roughly the same amount of time. However, both of those things may have been accelerated by my frequent fiddling with and removal of the earpads, in order to try some different foam inserts to better improve the headphone's seal.
Re sound quality... my recollection is that they had a somewhat narrow sound stage, but a fairly open sound for closed-back headphones. Those may sound like contradictions, but other folks here who are more familiar with those terms can probably do a better job of explaining why they are different than I can. The stereo imaging was also not particularly good imo, due to the imbalances in the drivers at different frequencies.
Tonally, the headphones are fairly neutral, but slightly warm leaning in the upper bass, and a little harsh or bright-sounding in some spots in the mids and treble, due to some unevenness in those areas. And they are fairly well-extended in both the bass and treble. These headphones use the same extended frequency titanium drivers as the K371 btw. So they have a somewhat similar sound, but with more warmth in the upper bass. And maybe not quite as much emphasis as the K371 in the sub-bass.
I used various forms of EQ to correct the tonal balance as best as I could on them. But it was exceedingly difficult without any reliable graphs to work from. Oratory recently added a plot of the K553 headphone to his new graphing tool though, so it can now be a little more easily compared to the frequency responses of some other headphones...
https://headphonedatabase.com/oratory?ids=219
You can add up to 4 more headphones (5 total) to the above graph by selecting them from the Headphones drop down menu. And also choose which target curve to use, and whether to display them raw or compensated using the various tools above the plotting area.
The main reason I got the K553 is because it was much more comfortable than any other pair of headphones I tried in the same or lower price range. (I got them on sale btw, for only a little over $100.) And I also liked their somewhat more open, warm, and relaxed, but still fairly detailed sound due to the good extension in the treble and bass than some of the other headphones I tried. Ironing out some of the less pleasing qualities in the mid-range and treble was difficult though. And took quite a bit of work on my part.
So far, I'm liking the construction of my 250-ohm Beyer DT-770's a bit better than the K553. But I've only had the DT-770's for about 5 or 6 months. And have run into a couple minor issues with them as well. The detenting on the DT-770's extenders is not very good. The 1/4" adapter plug was unreliable, and had to be replaced. And I wish the coiled cable could be detached and replaced with a straight double-sided cable. I've never liked the single-sided cables on any of these headphones.
The frame of the AKG K553 was fairly durable. But it was not an especially well put together design imo. And there were too many little things in it that could've easily been improved, or were just sloppy from a design standpoint imho. I got my money's worth out of them though... And then some. And enjoyed them quite a bit, after fixing alot of the minor issues in their design that bothered me.
Based on your previous comments, I suspect you'd find the design and construction of the DT-770 more to your liking than the AKG K553. Whether you'd like the sound as well, I have no idea. Because they are on the brighter side and also require some EQ-ing to produce a better sound imo. The drivers on the DT-770 are better matched imo than on the AKG K553. I actually went through several different pairs of the AKGs before finding one that I felt was adequate in terms of its driver symmetry. And it was still off enough that I had to use some corrective measures to improve the balance between the left and right cups.
The 250 ohm DT-770 also has a slight imbalance in volume between the left and right cups that requires a small correction. But it's more uniform across the frequency spectrum than on the AKG K553. All of the parts on the Beyer DT-770 can also be replaced if they ever break or wear out. And the pads are also washable in some soapy water. I have 3 pair, so I can always keep them relatively clean. Because the velour material does pick up quite a bit of perspiration and oil from your skin.