Huh I received my HD6xx 4 months ago and it came in the hard box. Maybe you get a different box depending on the factory it was assembled in? My HD6xx was apparently from Ireland.

I would say that it’s probably only true for the very early batches. My first pair had a driver failure but my replacement has had no issues despite treating them a bit roughly. But I don’t get the issues with the headband snapping, I doubt it’ll happen with daily use unless you purposely try to break it. The main issue is probably with the earlier batches having loose hinges which is what many reviewers have pointed out and I also experienced it with my first pair.

The hd660s were probably made just because the hd700 didn’t sell very well and they didn’t want to waste all that r&d work, so they stuffed it in a hd6x0 chassis. Hopefully sennheiser will make a proper successor to the hd6x0 lineup.

Hd58x and hd660s are pretty similar in the upper mids and treble. The HD58x are warmer and extend lower, so it’s basically an even more veiled hd660s. The hd660s does have more resolving ability tho. I would say that the hd660s is quite different from the rest of the hd6x0 line. The hd660s doesn’t extend as well on both ends compared to the rest of the lineup (hd600,hd580,hd650/6xx).