"Thought I might add a brief data point here. Received*a pair of fenestrated sheepskin pads today and have been running them on the HD600.*@Bill-P's intuition seems borne out by my experience. The net effect of the pads leaves the inherent neutrality (imho) of the HD600 intact. There's an impression of a slight boost in the bass, although I'm not sure "boost" is the precise term. The bass seems weightier, like it has more heft. It seems to hit harder. Overall the signature of the HD600 is thickened. The headphone still sounds forward but is vaguely more*polite. No sense of a weird sharpening effect, or an increase in shoutyness. Subject to change, of course, but the fenestrated sheepskin pads might be good for people who find the signature of HD600 a bit thin-sounding. I'll probably leave them on.
I haven't a feel yet for how the fenestrated sheepskin pads affect the technicalities*of the HD600. I'll just say they don't seem to harm resolution or clarity. I should note that I find them more comfortable than the stock pads.*
NB: Most of my listening has been done with the foam left in. The brief impressions herehttp://www.superbestaudiofriends.org/index.php?threads/source-av-meet-impressions.5748/#post-189887*describe the HD600 w/ fenestratedsheepskin pads and the foam removed. I listened briefly with the foam removed and, at least so far,have preferred it left in. I'll experiment more*withthat variable."