I installed cIOS, base 56(249), base 57(250), and base 58(251) using d2x v10beta53-alt-vWii mload v1.0
I tried using a Y cable, with the A port in the outer most port on the back of the Wii U, and the B port on the inner most, with 2 different HHDs.
One was NFTS, and one was WBFS, neither is...