As for stick in mud 600/650 diehards.......
Well, that could have been directed at me, I suppose, and given my contributions to this thread so far, understandably so. Given that, I feel some explanation might be in order........
Contrary to any impression that I might have given, I'm involved in this thread not because I want to be negative about the HD 660 S, but because I'm interested in it.
I'm a professional musician and have had a lifelong passion for audio. The fact is that I've had Sennheiser headphones all my life, starting with my first pair of hp's ever - HD 420 which I had in my teens, right through a whole line including the HD 560 Ovation II, 580 Precision, HD 600, HD 650 and HD 800. I even have the HDVD800! I could almost be accused of being a Sennheiser fanboy. The only other headphones which I have (and have ever owned) are some Sony professional closed back models (MDR-7509HD and MDR-7520) which I use when I'm recording for tracking, and also sometimes for casual listening from my iPhone.
Given that history the natural thing to do would be to order the HD 660 S without a second thought. But something has changed; the whole headphone market. There have been some very good posts recently on this subject (from donlin and others) and, as you've gathered, I'm also from that time and generation that well remember when the market was small, headphones a minority interest, and any new headphone release eagerly anticipated. Nowadays it's hard to keep up with the pace! The positive and negative aspects of this are something which have been discussed already, but unfortunately (and possibly incorrectly) I suspect that Sennheiser (and it would be quite understandable) has somewhat joined the rabble in the race to produce new hp's at an ever increasing rate. The fact that The HD 660 S seems to have the driver from the (relatively unpopular) HD 700 in an adapted HD 6XX frame, marketed with the now seemingly obligatory 'S' suffix (S, for what?), 'The legend continues' and 'Hi-Res' printed on the box smacks of...... well, I've said it all previously, so no need to reiterate.
But the real reason that I haven't simply pulled the trigger and sat eagerly awaiting the arrival of my latest headphone from Sennheiser, is that I'm genuinely not sure that I would like it. After the HD 650 came the fantastic, but arguably seriously flawed HD 800, followed by the widely unpopular HD 700, followed by the HD 800 S which was an unashamed attempt by Sennheiser to fix the HD 800's widely discussed problems (the first time that Sennheiser had done such a thing) followed now by the HD 660 S, which I suspect, at least in part, is an attempt to finally rid themselves of the 'Sennheiser Veil' criticism.
Add on top of this a very bad review from Tyll Hertsens and I'm (against my natural inclinations) not very tempted. Let me just say a few words about Tyll's review. I would not make his, or anyone else's, review the sole basis of a purchase decision. I don't even always agree with him, in fact I own and like a headphone which he thought was so bad that he didn't even give it a review! (the Sony MDR-7520). I know many pro musicians and producers who love this headphone and many people even use it for mixing! So, I don't take Tyll's word as the law. However, having read many of his reviews and having heard many of the phones which have been the subject of those reviews I feel that I have a good idea of where he is coming from, and as such his review of the HD 660 S has me concerned, especially with regard to the issue of it having a grainy sound.
I'm sure that you must all be wondering why I don't just buy it and find out for myself! Well, I might just do that, but I really don't like buying a headphone knowing that I will probably want to return it. But also, there's another reason why I don't think I'll like the HD 660 S, and this is the reason (finally!) for this post. I would be genuinely grateful for your collective help here! I would really appreciate it if those of you who have (or at least have a very good memory of) the HD 600, HD 650 and the HD 660 S, could tell me whether the HD 660 S is brighter sounding than the HD 600 and as detailed (resolving) than the HD 650?
Let me explain. I'm one of those people who prefer the HD 650 to the HD 600, and I not only prefer it's sound signature but think that it's a genuinely better headphone. To me the HD 650 is not only more natural sounding than the HD 600 (which is admittedly more neutral) but is also more resolving of detail, has better mids and better soundstage. In short the HD 650 is darker and smoother, but more resolving. Although it's a great headphone the HD 600 for me is a bit too bright and the upper mids a little to forward. This adds up to making the HD 650 more tonally accurate than the HD 600, and for me tonal accuracy (followed closely by resolution) is the most important aspect of a headphones sound. So, if the HD 660 S is tonally even brighter than the HD 600, and at the same time isn't (appreciably) more resolving of detail (not to be confused will treble sparkle) than the HD 650, then I'm petty sure that I can comfortably pass.
These things have probably been discussed, at least indirectly, before, but I would really appreciate your collective input on these specific points. For information I'm using the HD 650's in a few different situations, but primarily balanced from the HDVD800.
Sorry for the long post everyone. Barring responses to any replies that it get to this post, it will probably be my last in this thread - unless I end up getting the HD 660 S and come back to give some impressions. Thank you in advance!
) to answer my questions. And don't worry, I didn't take you comments at all personally(!) and as I said, even if they had been directed at me they were probably justified! 
