[tomb]

If the 580 to 600 to 650 were incremental improvements and each was definitively better than the previous model would the conclusion of that not be that the only one that could be recommended in 2023 would be the HD660S2 ?

That logic also seems to defy the personal preference and subjectivity that is fundamental to so many aspects of this hobby.

The 660 series are a diversion due to portability/impedance limitations in the market. As in, the 300 ohm nature of the 580/600/650 (and even the 800) don't meet the requirements of the greater, non-audiophile mass-market.

Yes, Personal Preference and Subjectivity defy Logic.

It would probably take the wayback machine to find it these days, but Tyll Hertsen's excellent InnerFidelity site did extensive reviews on each. Amazingly, Tyll even stated in the same sentence that he preferred the HD600, even though the HD650 was more refined. If that doesn't defy logic (and real-world testing), then nothing does.

None of that means the HD600 is the better headphone - to the contrary and with tested results, instead.