I might just do that! Of course, listening oneself is the only way to know if you like something, and I'm glad for you that you like yours. However, I feel it's accurate to point out that any 'technical-up-to-dateness' which you perceive is self induced (placebo). The facts are that Sennheiser has taken a headphone housing which dates fro the 90's (6XX series - nothing wrong with that) and a driver from another older headphone (HD700 - nothing wrong with that either) and modified the baffle from the 90's design ever so slightly to accommodate the different driver. Not exactly a new technically up to date innovation - just extremely good business practice. Nothing wrong with that either, as long as you think it sounds OK. Technically better than it's predecessors? Very slightly extended frequency response range? Very slightly less THD? You can't hear those things. If you think it sounds better then it does, but it's not because it's more technically up to date.
What annoys me more about the HD 660 S than anything though (and again, irrelevant if someone thinks it sounds OK) is the way that Sennheiser (a company which I love, btw!) is marketing this bin part headphone. 'The legend continues' - that immediately makes me suspect the opposite. And why is it that every recent new release from Sennheiser has to have the 'S' suffix? If I was being cynical I would accuse Sennheiser of cheap marketing. But the thing that takes the biscuit for me is the 'Hi-Res' sticker on the box. I'm afraid that hi-Res is just a load of BS and Sennheiser surely knows it. Many people on this forum probably don't know it, but it is, I'm afraid, just marketing BS.
I'm sorry, pietcux - this rant is not directed at you - your mention of the new hp being technically up to date just lit the fuse! If you want to know why Hi-Res (and to a large extent most considerations of what the latest technology is) is just BS, have a look at this:-
PS I sincerely hope you continue to enjoy your new cans!
Watch to the end!