Refurbished my Sennheiser HD700 headphones by replacing the ear pads ($81), Headband cushion ($29), and getting Moon Audio's 10-foot balanced
Black Dragon cables ($370). For the price of those cables, I could have bought the above phones, but I wanted my HD700 phones as I simply love their spaciousness. Something I not sure the 660S2 could match.
Anyway, listening to these now, that was money well spent. Mainly listen to music, mostly jazz but just about anything. These phones sound better than when I first got them, even after break in (if you believe that sort of thing). Bass response is slightly improved, soundstage is about the same as with the original cable (now destroyed).
BTW, what Moon Audio aims to do is match their cables to your headphones, and the Black Dragon cables are tailor made for the HD700 phone's sound signature... Here their aim was to tone down the highs, specifically around the 7k freq. as the biggest complaint around these phones is they're too bright. They certainly did that, and without killing the soundstage. Overall, they are warm sounding with a bit more detail compared to the original cable.
The killer is the expense; though do note the base price of the Black Dragons for the HD700 is $275 for a 5-foot cable with a single TRS end. I paid $370 for a 10-foot balanced cable with dual TRS connectors to work with my Teac UD-503 DAC. As shown below. Though the cables shown there are from Surf Cables. I paid $160 for a 6-foot cable, but to be frank, they never moved me. I still have them, but they cannot compete with the Black Dragons. And still preferred the OEM un-balanced cable over them.
Anyway, I'm happy with my refurb, and especially since the Black Dragon cables now breath a warmer, more detailed sound into them. Lovin my HD700 even more now.