Also on my rx580's setups i never plugged the sata pow and got up to 10x cards detected and working..

Make sure when your plugging your risers to do so in and order per one.
For example first plug the black slot. Boot windows and check everything..
Then start with the white slots one at a time..boot windows check..
If that works proceed like that until all your cards are detected.
Also. For the 13x setup you need 5x nvidia mining only cards and i think will only work with linux based OS.