Believe or not Naruto is the 2nd SO6P and if he isn't show me proof that he is not the 2nd Sage of Six Paths
This argument is a circle, it's the exact same argument used for and against the existence of God, You can't prove he is, we can't prove he isn't.
It is more likely that Naruto has remnants of the sages power, but the Bijuu's are talking about his personality more than his ability. He never gives up, and he strives for peace. He will work with someone and refuses to force them int submission, this is how the first sage has been portrayed.
So I think that is what the Bijuu's are talking about, rather than him having a super, secret, special power. He is, without a doubt, an incredibly strong ninja, but this has happened before, Hashirama, Minato, Madara, all incredibly strong. The difference is that Naruto has a will that none of the others have shown throughout the whole story so far. Minato would consider killing Sasuke, Hashirama was seen to have killed Madara. Naruto will only kill if it is the last option - in his mind no one life is worth more than another. That, I believe, is what the see in him, and what the sage passed on.