I think I should correct what I said before. The fenestrated bring it more in line with the Amiron Home in signature, but in all honesty, comparing both side by side I can't say the Amiron is better. The HD660s is more relaxed sounding and doesn't suffer sibiliance (try 'Close To Me' by the Cure on each and you'll hear what I mean). They're their own thing and both great depending on the song that matches their strengths.
This is my 2nd pair of HD660s, the first pair sounded lacklustre in everything but vocals. They just weren't detailed, I sold them earlier this year. This 2nd pair are more detailed. I noticed this 2nd older pair were made in Ireland, the 1st pair weren't. Has anyone else experienced this difference in the 660s?