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I heard silver box HD650,black box 650,600 and 660S.I like the 660S most but they are all amazing,the old 650 was too dark and had muddy high bass but it had best mids and best transient resolution.The new HD650 have peak in high treble 10-15 KHz and is much brighter,more sub bass and less muddy than old HD 650. The HD600 is most neutral headphone I ever heard in my life,some people say it have shouty upper mids but I didnt hear any of that.If I couldnt use EQ,these would be best headphones for studio production and mastering,they are incredible,I cant find any fault in them but I have to admit,I love the seductive warm sound of HD650. But what about HD660S? Why do I like it most? It have most pleasing treble frequency response and bass,it seems to have less upper bass,and more sub bass,also the soundstage seems tiny bit wider but I am not sure if it is due to driver difference or its just illusion due to different frequency response.Its treble seems more airy,I think the Sennheiser veil is real,the latest versions of HD600 and HD650 have this veil reduced to almost zero but little bit of it still remains,the HD660S removes that last bit of the "veil" and it sounds delicious.
Read InnerFidelity's analysis of the 6xx range, they're all different, for Massdrop to sell a "6xx" headphone would be awful, because which model is important.
I'm interested in hearing the 660's, but I've only listened to my 6xx's vs 600's. I listened to them both in one setting with some pretty good sources and amps. An Oppo HA-1, a Jot with its onboard DAC and the HA-1 as source, some lesser Schitt stuff with HA-1, and I came away thinking I was happy with my $199 drop. I do like the warmer fatter low end, and greatly prefer the colour of mine. I think if I had to do it over again I might lean toward the 600's as they were a bit more neutral, thus my vote. When considering price though (and aesthetics), I'd definitely go 6xx. Neither being good reasons to buy hifi.....
To give an idea of where I'm coming from I traded fully aktiv Linn Majik 109's for fully aktiv Linn Ninkas. Translation: I like mellow. The 109's are incredibly revealing, but the Ninkas just rocked better while still being world class transducers, and most importantly could be listened to for hours, like the 6xx's.
I now have a Massdrop cheapo Aune X7s (XLR out) fed by either my Oppo 105D (the same DAC as the HA1) or my Linn MDSM/2, because neither, superlative boxes by any standard, can drive the Senns as well as they can go with only their own puny headphone outputs. So yes, you've gotta get an amp.
BTW, HD6xx's sound pretty darn good straight out of my LG v30+ (which now has a bootloader exploit!)!
bring them back
Every hard-core review of the HD6 series specifies disappointment in the 660 S. Inner fidelity was blatantly disappointed in them, citing lack of stage and depth, along with shallow low end with harshness in Highs.
WILLxLOVE
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I agree with tyl I tried 600 650 and 660 and i find the 650 sounds the best
Any one care to explain why 650's has more votes than 660 S? 660 S is the successor and improved version of 650
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SkyyM
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HD 650 a legend for how musical it sounds with almost any source.Its not neutral and lacks a bit of bass but the soundstage and bloom is incredible.HD 660's just read the online reviews you will find out why it's somewhat a disappointment.
SkyyM
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Its becose Marv from SBAF and Tyll said they dont like it so all the people who worship them like gods and take everything they say as ultimate truth without hearing the headphones for themselfs and making their own opinions started repeating what they read on internet. 1. The allegations of inferior soundstage is pure BS. 2 . New HD650 have much harsher treble,it have quite high broad peak from 10-15 KHz,it sounds unpleasant with pink noise but I still would not call it harsh headphone,660S dont have this. 3. Marv wrote it had inferior resolution to HD650,again,I found no such thing. Never believe what you read on internet,always create your own opinion by trying the headphones for yourself.