I used to use these with my Martin-Logan CLSs and they were great. I told HP about them and so The Absolute Sound did a review of them, which was quite favorable. They are solid copper (or silver) ribbons. Weren't very expensive, for the copper, back then. They have fallen off the map somewhat, but maybe you can contact them and see what you think.
-docknow
https://bridgeportmagnetics.com/3-functions-of-goertz-cables/