Board Thread:Episode Discussions/@comment-1251315-20160721110532/@comment-1512913-20160722115026

That's true, meaning Six Paths Senjutsu alone isn't enough to use Truth Seeking Balls. All Six Paths Senjutsu does, besides boosting one with Senjutsu chakra like Sage Mode presumably, it gives one omniscience and omnipotence of chakra, allowing one to use all chakra natures and an innate grasp how to do so.

But as you say, SPSM alone didn't activate the TSB, only after he entered TB chakra mode they appeared. One of the novels apparently states that TB chakra was needed and if possibly non-canon novel is not good evidence, then a databook says that TSB are akin to Tailed Beast Ball. To my understanding, TSB is a Tailed Beast Ball containing Senjutsu chakra and all the chakra natures inside, which can be combined variously at will for various effects.