Boy oh boy, I'm sure eager to get my hands on the HD660S. I'm a big fan of the Sennheiser house-sound and still own a good number of Sennheiser headphones, including the HD800, HD700, and HD650, to name just a few. Lately, however, I've been using the Audioquest Nighthawk quite a bit, mostly because I love the NIghthawk's sumptuously dark and non-fatiguing sound-signature, though the bass could be a bit tighter and the upper-midrange could use a bit of a boost. It sounds like the HD660S improves upon these two points, but I wonder: Is the HD660s as silky smooth and non-fatiguing as its predecessor? As the Nighthawk? Any opinions would be helpful. Thanks, Y'all.