dioporksI personally like the 6XX for what I paid for them when they first released, but after researching the 620s further - came to the conclusion you shared.
Both produce music and are conduits for a good time; I prefer both the tuning and performance of the HD 660S2. It could be my “one” headphone. But if I only had HD 58X Jubilee money… I would be hard pressed choosing between the HD 58X Jubilee and HD 560S.