Yes. I own both the 6XX and the 660s and I actually have my 6XX cable on my 660s as I type. The Sennheiser 2-pin works with the 580, 58x, and the 600/650/660s. Same with the pads headbands, grilles and even driver assembly (excluding the 58x which have different drivers. Unsure about the baffles.)
Will this be in stock again? I really need this cable, the original on the Sennheiser website and the ones of my local tech shop are always sold out...
From experience, sometimes you can call Sennheiser support and they have stock even when the site says it’s out of stock 😂 or at least they can give you an idea of when it will be back.
Drop routinely brings different vendors for HD 6xx and HiFiman cables back in stock. I suggest you click the “reminder” button, to be reminded when/if Hyper Design comes back in stock, but also use the search button sometimes because 3rd party Sennheiser cables are often rotated into inventory 😊 I have like… 4 or 5 cables that work with Sennheiser’s HD 600 series 😅
6N purity copper is nice! Nylon wrapped, these may feel a bit like the high end HD 800S/8xx cables. I haven’t tested this brand specifically though.