I am not a big fan of mixing and matching cables. I prefer to have all one brand. That said, Cardas is not a great match with ARC. Shunyata and Synergistic are both good matches. I have all ARC Ref gear and use Shunyata Zitron Alpha HC power cords. They are excellent. The Synergistic always seemed a bit gimmicky to me. I have a couple pairs of their interconnects. I have not compared their power cords. But I have found both Shunyata and Synergistic interconnects to have a similar type of sound. Really both are quite good.
I am surprised that the GSi75 does not have a 20 amp socket. My Ref 110, Ref 5se and Ref Phono 2se all have 20 amp sockets.
BTW Be careful buying used cables, there are a lot of counterfeit cables around. Shunyata will verify that a cable is real and not a fake for you. Just call them with the serial number. World class customer service.