There quite possibly could have been issues with the first batch of 660S that was soon adjusted. I was late to purchase one because of all the noise on this forum that put me off, I'm glad I changed my mind because this is an excellent headphone and always gets used even with a HD800S on my desk. I still stand by my statement that 660S is more revealing than 650 because I can hear the differences between DACs quite well on this headphone. It can go from dull, slow and hazy to clear, fast and dynamic. Put a chord dac in the chain and you get an amazingly clean, articulate and smooth treble.