From memory:
The Zu damn near has it all: best sparkle, resolution, dynamics, and bass. Basically you up the musicality, fun-factor, and resolution. The Equinox was lacking serious fun factor for me....tonally it sounded like the stock cable and that's not what I was looking for. Some swear by the Equinox though...maybe I didn't give mine enough time. The Silver Dragon I've only listened to briefly; it was pretty impressive though. I rated it just a
hair behind the Zu, though it may exceed it in some areas.
I sold my HD650 and all cables (additionally owned the Cardas, Clou Red, and Headphile Black Silver) over a year ago, but now I have the Senns heading back to me

This time I'll have the Zu, Silver dragon, and a Blue dragon (which I've previously only heard directly out of a Benchmark DAC1 in balanced configuration). This time the HD650 will only be used with vinyl
For my tastes it looks like the Zu and Silver Dragon are it.