Obito and Nagato got injected with those black rods.
Madara and Obito used Gedo mazou without without the rods.
I don't know what other outer path technique you can use, but to revive and use the six paths through them.
Yep, Pain is an example.So u can use outer path with them blacl rods
Hagoroma didnt have 2Yep, Pain is an example.
He used the black rods in the body to use the paths.
Madara told/taught Obito to use the six path Justus with the black rods too.
(I guess it was because he didn't have the rinnegan)
It was in chapter 606 page 14, 15, and 16
Hagoromo had the eyes, Obito didn't have them at the time.Hagoroma didnt have 2