As I understand John Grado voices his headphones listening to vinyl, that's the reason. I think the special editions are voiced a bit more for digital.
Loving my hf2's, now I really don't know what amp to get for them.
The source I have now is a TC Electronic Konnekt Live (detail oriented source). It's integrated headphone amp has no chance to drive Grados well. It's too high impedance, too powerfull, no bass control, kinda bright (yes, with hf2's). I've put maybe 20 hours of burn-in in them, no change so far.
My amp short-list: CEC HD53N (and balancing the hf2's), Gilmore Dynamic V2 (if I can find one), Berning MicroZotl (if I can find one).