Well, I'll be... If it wasn't edited, then indeed, they haven't stated by how much. I still didn't expect such a departure from what was initially reviewed - see the review conclusions in the product page (balanced, no booming bass or boosted treble, brighter than the HD650, veil not so prevalent etc.). But since we're splitting hairs, they requested "an increase to bass extension", not louder bass overall. For reference, see the better *bass extension* of the HD660s, without the big raise in the 50-200Hz territory. That's what better bass extension would mean, if you want to debate wording.
The fact remains that they'll have a very different sound from what was initially reviewed and they'll definitely be dark.
To explain why I joined this talk - basically what I expected after reading thoroughly about this product was a balanced, neutral headphone, not very different from the HD600 but easier to drive, at a very enticing price. And in all fairness, that's what was marketed (see product description, specs and reviews).
As I've said, I get that some people will like them better this way, and that's only natural, everybody has their own preference and specific intended usage. I simply think it should've been marketed as a different product (HD58x-B or such) and not make such a radical change to the product that was reviewed initially and for which we (or at least I) joined the drop.
In the end, I guess I'm waiting for the final reviews and see if the mods don't involve radical changes, soldering, warranty voiding etc. There might still be the promise of what I joined in for, going by the "more elaborate article in pdf with some interesting modifications for those that seek HD600 type of balance" that Solderdude hinted at.