I compared the similar-to-HD-540 HD 530 to the HD 600 and thought the latter sounded a bit more detailed but a bit worse in timbre, with my preference being the HD 530. I also compared the HD 530 to the K 701 and thought they were about even. These HD 530 were slightly modded, however.
But while old headphones can sound quite nice, we really aren't getting that much for our $, £, and € with these 'modern' headphones like the HD 600 and K 701, either, so I'm not sure that the comparison isn't a bit skewed in favor of the older models.
Edited by vid - 3/21/14 at 5:48am