I'm new to this forum, but think I have a few details to contribute to this thread - which I do out of appreciation, as this thread has been of help when acquiring my own MDR-v6's.
I now have both a genuine pair, and a fake (without a box) for which I was refunded. So I want to note that the fakes can have "for DIGITAL" stickers that look really good. Those on my fake were not blurry at all, and if there is a difference, it's so small that unless you compare very carefully side-by-side with a magnifying glass, you'll probably not be able to notice anything. If I had only one of the pairs to look at, I would not be able to tell by the stickers which was which.
When I only had one pair without a package (the fake, sold used by a U.S. Amazon seller), the only clear signs of it being counterfeit were these three: 1) The headband was wavy, not smooth, on the inside. 2) Opening it up, the drivers were unmarked. 3) The sound - as mentioned in the initial post, it lacked in the highs and the bass was a bit muddy - a "meh" experience.
Later having both side by side - after buying the real (and then unused/still boxed) pair from another U.S. Amazon seller - I saw in addition that: 1) The cable was coiled in tighter loops on the real pair. 2) The text above the stickers reflected light a little bit differently on the real, the reflection shifting as the angle is shifted. This may however simply be because the real ones were unused, and perhaps a little bit cleaner and/or less worn. I wouldn't count on it as a sign.
Obviously, signs can disappear with new fakes, so the lack of a sign (e.g. blurry stickers) cannot be taken to imply genuineness. Everything significant has to check out.
Some imperfections can however occur with the real ones. E.g., seen on mine, the left sticker is applied at a bit of an angle - that's the only imperfection I can see. (I saw another member mention this regarding his MDR-v6's in another thread, so perhaps this is a batch "problem".)
Final note on the sound: Having and comparing the two, my ears agree with those of the initial poster. The description however also made it possible to tell the fakes were fake even before having the real ones. And now having the real ones, I appreciate them.
Anyway, thanks for the info, which came in handy as I bought mine, and I hope the above will be useful to someone.