Just my ignorant opinion, but when I compared a pair of 32 Ohm DT880 to a pair of 600 Ohm Beyer DT880 I had a really hard time telling them apart.
The 600 Ohm version seemed to have smoother treble, but that was about it.
Maybe it's just me, but despite what Beyer says, the 32 and 600 Ohm versions sound almost identical.
I haven't heard the 32 Ohm DT880, to be honest, so I can't quite comment on that.
And I'm not implying that there is necessarily a difference between the 250 Ohm and 600 Ohm DT880... but the DT880 600 that I have right now does sound very smooth and slightly dark compared to the Pro one that I heard earlier.
Now if we were talking about the DT770, I would honestly disagree that the 32 and 600 Ohm versions sound "identical", simply because they have different dampening properties. I have not found a real reason to open up the DT880 yet, so I have not investigated that, but if what I found for the DT770 applies here, then Beyer does damp some of their headphones differently. Perhaps it is that difference in damping materials that causes the differences between these headphones.
Plus... tonally, some headphones can sound almost identical (like the DT880 does sound very much like the HE-560), but when the right source material plays back... the difference would still become apparent.
On the other hand, though, the number of tracks in my music collection that can reliably show that the HE-560 is above the DT880 is about 30%... so that says something.
Benefit of the doubt but... he did say it was the Pros and that one seems to have a confirmed variance (Mainly due to clamp but hey, it's a difference.).
Tightening the clamp on these DT880 600 doesn't make them brighter. In fact, it makes them even smoother, and sibilance is even less pronounced, though not at the relaxing level of my ES10 or HE-560... It's still very bearable compared to the last time I owned a DT880 600 + O2 combo.
The DT-880 I had a long time ago was one of my favorite headphones. This was the 2003' edition with the flat grills. The Pro version we heard during our mini meet seemed a bit bright to me. The treble just wasn't as controlled. I will however, agree that the 600 ohm version does control the treble better, and sounds overall more resolving. Have you tried it out of an OTL amplifier? I personally think the DT-880 600 ohm is one of the best headphones that Beyerdynamic ever produced. The newer Tesla models sound terribly harsh imo, and I think the DT-880 is what I'd return to if I ever decide to pick up a pair again.
To be perfectly fair, I have heard good pairs of the new Tesla models, and when they are good, they are... quite good. This DT880 600 that I have here still surprises me because it's not just smooth and resolving, but that it has a certain lushness to the sound as well. I don't think anyone can call this headphone "harsh" by any standard. Even the very rare sibilance it produces is a soft sound rather than a sharp piercing sound.
The whole presentation is softer and more polite than the usual Beyer sound... and it just makes me wonder how I have missed this... since I have owned and auditioned the DT880 600 quite a few times already, and it has never quite sounded like this. Even out of a good OTL amp, the DT880 didn't quite sound this lush. This is out of a solid-state amp, no less.
And since you know me, I think you'd see that when I say a headphone is "dark", it really is quite dark. My standard of neutrality is typically darker than most folks.