I am also interested in this pairing. I bought the Cobalt and I am looking for a good headphone and the 660 S is one I am looking at.has anyone used DF cobalt with Sennheiser hd 660s? In theory there is enough juice but i m affraid of the harsh treble. I never listened to hd 660s but read that it s brightet then hd 650 and i m wondering if the pairing with ESS dac will sound too disturbing to my ears.
i alsoread that cobalt tames bright headphones but it didn t happen with Beyers which are treble beasts.
A person who has had both told me that they have a perfect synergy, but I would like to hear other opinions.