Looking at the graph, he treble doesn't seem to be tuned down, it's about the same, only with a boost in the 5kHz area, where the HD650 were lacking, so it's really improved. And the bass seems about the same too, only the midbass seems a bit reduced. We will see comparison graphs soon... I've got some 5 year old HD650, so I'm really interested It's a matter of time untill a cable snaps or some piece plastic breaks so I'm strongly considering a HD660S for upgrade/backup, to use them in paralel. I've tried this move with the HD700, but they were an utter fail, plastics crackling in the earpads, treble peaks, bass with the sound of an empty barrel. Got rid of those. Yes, they had a little more resolution and treble detail than HD650, but the drawbacks were terrible. And the price too high for what they were offering. The paint that doesn't chip off in the first cuple of months (wow, took them long enough to figure this out) and the 5kHz boost over the HD650 are the main selling points for me compared to the HD650, the rest seems about the same, which is good, there's no reason to change a good thing. Maybe a little more boost in the 10kHz+ area, but c'mon, all headphones in the market have worse weaks spots, frequency wise and otherwise.