But audiophile headphones like the Sennheiser HD 6XX go another route ... Of the ones not already mentioned above, the HD 560S ($230) and HD 660 S2 ($600) are the most compelling.

and the HD 505 sits just beneath the Sennheiser HD 600 in the line-up. Sennheiser says that the new headphones have an adapted transducer that was designed to give better bass and treble extension ...

Generally speaking, 500-series headphones have enjoyed wide frequency ... Perhaps the most compelling alternative, though, is Sennheiser’s own HD 600 – they’re a step up in performance ...

However, as I mentioned further up, you can get the Sennheiser HD 600, which are the 'step-up' versions of these headphones, for very close to the same price as these in the real world.