Oh I definitely agree about good driver dampening on a headphone, I'm actually kind of particular about the drivers the headphones I buy have. To me the HD 660 S is an evolution of the HD 700 despite the different tuning and honestly seems to be the replacement as the HD 700 was discontinued. Some headphones with good/great drivers do have some questionable/unorthodox tuning, looking at you Nighthawks(and a few others too).
"You prefer soft drivers, right?
Yes, that’s what we use at Sennheiser. Now, a softer diaphragm on its own can have resonances in the audible range. So we add a damping material to the driver — it works similar to a car door. If a car door were pure sheet metal, you’d hear a crashing sound every time it closed.
But with dampers, you get the nice sound that a door should have. This is how our dynamic drivers behave. You just hear the basic impulse, not all those grating high-frequency resonances"