Got my pair today and listening now. I am definitely treble sensitive but this one isn't as spike-to-brain bright as the 770, 880, or 990. May eq down the peak just a bit. Isolates better than expected. Better than the 770 which I thought was fantastic as a passive isolating can with velour pads. Imaging is fantastic. Danny Brown's "Theme Song" really shines on these. Strings and whispers and background sounds now have a platform to stand on. Mids need an eq boost I think. Bass is just a bit muddy, but nowhere near the muddiness of the 770. Punchy and fun. Does not sound excessive to these ears. Forgiving of some poor recordings, others not so much. I listen to a lot of garage, punk, delta blues, mid century gospel, etc, so it's important to me that a headphone is not too transparent with crummy recordings.
The 6XX has been my main can for about 18 months so this is quite a change of pace. I think I dig it. I bought them bc I work from home and need to mute out the neighbors, so we'll see how I feel rocking these 6+ hours a day. For $390 it's a pretty tremendous value if you don't hate the sound signature. German made, very attractive in a minimal kind of way, two cables, two sets of pads, nice case. Does a ton of things really well. I like the Beyer sound when it's held in check just a bit, and I think these can be described that way.