But the 660s has the worst sub bass response of any of the 6x0 series... How can it be preferred for professional work over the s2, 600, or 650? I can understand the preference for the tame treble. Personally, I find the s2's treble to be much clearer, but I can still understand why some people say it fits the 660s's sound better.

> HD600's warmth and relaxed vocals (the mids being farther back, as you said)

What? The 600 has the most forward mids and least warmth of any 6x0 except for maybe some versions of the 580.

There is nothing wrong with preferring the 660S over the others in this lineup. There are some songs where I would still prefer the 660S over the S2. Everything depends on what you like.