AKG240mkII: Unfortnuately, for you reasoning, the 80Ohms and 600 Ohms have been used on two completely different setups, and I have confirmed the problem with the 600 Ohms with a different setup. The 80 Ohms I blew by listening to Deadmau5 far too loud for far too long.
I will return these (again) tomorrow and see what happens. If the problem still remains I will set them on fire outside of the store and tell them to go to hell.

Update:
Instead of going back to the store I took the left can apart and just twiggled a bit with all parts. Now the distortion is completely gone.
What worries me is that even though it works now, the distortion might come back.
I really like beyedynamic but I don't know if I am willing to buy another pair from them.
I also find it remarkable that the QC is so poor at beyerdynamic. But then again, this isn't the T1 and maybe I'm just an unlucky punk

Maybe it is your now half- deaf ear that is distorting? Loud is fin, but please don't become the old man saying: "What did you say sonny?"
I have these headphones and cannot ever hear distortion unless way overdriven. Very good sound quality - even a nice sound stage for closed cans!

I have been using a pair of these for about a year now so I guess they are well run in. I would agree that they need careful placement on the ear and if you get them slightly off then the SQ suffers but I have also found this with other on-ear designs so I can't necessarily fault them for that.
Provided they are on ear I get a perfectly good bass level and I listen to some very dark ambient sounds from the likes of Lustmord that would be practically silent without some bass. Maybe they are slightly more picky about how they sit but I don't experience any of the problems that some of you seem to have. I enjoy the sonic signature they give me and I think they compare well against my HD-600s at home.

All Beyers I owned required very long break-in to show their best; and yes, out of the box none sounded good.My DT990/600 Ohms only stabilized after 350+ hours (harshness was gone, bass increased to the level I did not think they would ever have, clarity improved, etc.).My T90 are even more so; at this moment I have somewhere around 150-170 hours and they just started sounding with almost no harshness (bass is still weak but keeps improving - very slowly).Other than that, *right* headphone amp is extremely important; Teslas are notorious for not accepting some amplifiers. For example, only my Musical Fidelity M1HPA can drive T90 properly (extremely well to be more precise). MF V-CAN II cannot; even new Asgard 2 produces somewhat muddy sound with them (although none are broken in yet so that's not set in stone).For comparison, Asgard 2 makes D990/600 shine (the best sound I could ever get out of them), so does MF V-CAN II.So if you don't like sound - try a different amp. You might find you would have to go to better amps until you can hear them sound right.I am expecting T50p tomorrow so will update on how they perform in a while.

Hmm, where is the Unlike button?

I'm going to try it just as a DAC next week, I'll let you now how it turns out. A lot of the drawbacks might be related to the headphone amps.

FYI, the uDAC2 is quite good when I use it only as a DAC. It sounds really good when I hook it up to my headphone amp and my HD650.

Good to know, thanks a lot. I don't use headphones, so it's a relief.