A few months ago I made a theory that the Rinnegan is needed to activate Perfect Susano'o. Many know-it-all wannabe members bashed me for it saying its EMS activated. Well you are all proven wrong. As shown in the latest episode, Madara can not jump from any variation of Sharingan to the Rinnegan. Hence when Naruto attacked him with the massive Rasengan Madara went into EMS and used a LV2 Susano'o. Why? He could not go from the Sharingan to the Rinnegan. He first had to go through EMS. It's clear now that Rinnegan is needed for PS.