when i buy R10 #365 it already come with that cable.
the upgrade cable is by TOXIC Cable UK where you can contact their company through head-fi.
the cable and the workmanship is 700pounds according to old post about R10 #365 on head-fi,
which also mention the cable it self is a high grade silver plated copper cable much purer than the original R10 cable with furutech carbon balance xlr connector and its xlr to 6.3 converter
Sound-wise, it doesn't change the overall sound signature of the R10 but just improve it with more detail and extension on soundstage/tighter bass and slightly more refine treble giving a more euphony to the headphone.