Ah, you are putting me on the spot . I think the balanced cable I made for the HD600/650 was made from continuous cast copper with a Teflon insulator. The stock HD600 cable is whimpy enough that just about any other cable makes an improvement. We sold the Cardas single ended HD600 cable for a while. It was slighty modded with a right angle TRS plug and it was quite a bit better than the stock cable.
At Can Jam a couple years ago I got to hear the then brand new Cardas balanced cable for the HD800. I thought it was a nice if not huge step up from the quite good stock HD800 cable. Recently I built a balanced cable of my own - maybe from Mogami mic cable? Can't recall. Anyway, the difference between it and the stock cable was again not very big.
I was just curious that's all ,my apologies . I bought some 20 GAUGE silver plated solid copper/Teflon insulated NOS hook up wire for Crack and was wondering if this is good choice in case I want to build my own headphone cables