IMO, the HD 800S is still worth a listen
@MalinYamato, if you get the chance. Both the HD 650 and HD 800 were a surprise for me the first time I heard each, because I had gotten it into my head that they sounded a particular way based on reviews (the HD 650 was “dark, very colored and veiled, with muddy bass bleeding into mids but weak treble” and the HD 800 was “bass-shy and fatiguing in the treble”), but my actual experience with them was much more balanced than I expected (HD 650 surprised me with its detail retrieval and not overly resonant nor muddy sound, while the African chorus at the beginning of “Diamonds on the Soles of her Shoes” obliterated my preconception that the HD 800 would have no body and no bass impact). You may still find the HD 660 S to suit your preferences, and I find it easy to enjoy for a long time, but
@pietcux is right the HD 800S is a step up in sheer performance (like how the HD 6 series is a step above the HD 5 series). It may surprise you.
I hear ya... some headphones just don’t have particular hype around one aspect that really makes that one thing stand out, and unfortunately that makes them less memorable. The “legendary” HD 598 (at least among gamers) and more recent HD 599 have a fairly noticeable dip in the upper midrange that makes them seem more laid back with a bigger soundstage (especially combined with the 15° driver angle), and the bass is also slightly more “full bodied” by having a tiny bit of blur around the low notes. This emphasis on soundstage and midbass might be more “mainstream” than audiophile (and when you’re making art, who is to say what is “correct?”), however it was very memorable and well loved. The HD 579, by contrast, was a little more flat, and though it was a new tuning for the price range it just didn’t capture people’s attention as much and it didn’t sell well, ending up being discontinued. I think the community might be ready for a more “reference” HD 500 series headphone some day, but Sennheiser will have to be clear about the appeal of such a model.
For me, the HD 650 is like Coca-Cola while other manufacturers go for a “Pepsi” experience. Pepsi would often beat Coke in taste tests because it was obviously sweeter and a bit more exciting. Coca Cola tried the “New Coke” flavor that was also sweeter, and though “Coke II” continued until 2002 (did you know that??), Coca Cola Classic was brought back after only one month away from shelves because people realized the original taste balanced better with a meal, and was easier to enjoy a whole can over a longer time drinking (Pepsi and New Coke were best sipping as a dessert). I have a few fun planars and some “fun” closed headphones, but after an hour or two, if I want to keep listening I end up switching to the HD 660 S or HD 650. The HD 660S is just a bit more energetic and charming from the start, but it’s still refined enough that I can listen for the long haul.
I’m amused at the idea that a pair of headphones might have a “vintage” like bottles of wine. But, as
@HipHopScribe pointed out, I have a direct line to Sennheiser’s A-Team (Audiophile team) and they confirmed that the drivers are still made in the same Ireland factory as they have always been, to the same famously narrow tolerances as always. It’s possible there were some other factors at play, but anyway it’s cool you found something you enjoyed (and enjoyed the HD 660S enough to buy two!)