Board Thread:Naruto Discussions/@comment-26508646-20150704031517/@comment-25442883-20150706125832

@TheSooped totally agree with your theory, i was thinking the same in fact. It is nowhere mentioned that he need power of beasts for SPSM.

We know that ones who have all 9 beast chakra inside them and using their power they got marking on back, ability to fly and truth seeking balls. If Naruto lost their chakra he lost access to these abilities, not SPSM.

After being 'revived' in war he used Lava release Rashenshuiken in SPSM and latter enhanced it with chakra of beasts thus gaining tsb's, ability to fly and those markings. In gaiden he used SPSM and enhanced it with only Kurama's chakra. Base implication of SPSM is lack of marking around his eyes.