I think burn-in makes audible change on this headphone but one aspect can be unit dependent. My first HE-560 didn't have a piano grain but this second one did. After burn-in, no piano grain and the bass developed.
That's not why I'm writing today though. Something worse happened than grain this weekend...Sub-bass rattle in the left driver. Thought it was harmonic distortion at first because it didn't sound like how my first HE-560 rattled but then I realized it was the driver making the noise, once again. Back to square one and I'm not sending this one back. It was straight from their supply store, so recently made I'm guessing. It's mainly noticeable on quiet sub-bass, so A LOT of the time. I wasn't aware of this issue from the reviews so I added a note in mine as well as how to fix it.
According to jerg, sealing the pads to the driver from his mod fixes it . My amazon order for the glue is going to take longer than expected so I'm gonna have to go to the local store if I wanna get it fixed this week. Minus half a star from my review until it's fixed. I'm being generous because the sound unhampered really is incredible at this price. And not to doubt jerg but If it doesn't....I'm gonna get mad a. A problem like this shouldn't exist at this price point, in high end products. Shouldn't exist even for lo-fi.
So, all in all, if it works for me then jerg's mod has an objective benefit for the HE-560 irrelevant of sound preference. Thus blind comparisons won't matter for this.
Hope this helps other people as I don't think many are aware of this.