I dont think it is altogether necessary for us to use via negativa language. We can point out that to those who knew the Buddha personally he was supremely kind, calm and compassionate. While these qualities could be discerned objectively, it is clear that there was no identification on the side of the Buddha with them. While we always say something from a conceptual point of view or at some level rest our way of perceiving in some kind of axiomatic paradigm, the Buddha did not. This is why the Buddha could not suffer. I think that this is all we need to know about the Buddha and his doctrine.
PS: I still delight in all the doctrinal formulations.
"Beautifully taught is the Lord's Dhamma, immediately apparent, timeless, of the nature of a personal invitation, progressive, to be attained by the wise, each for himself." Anguttara Nikaya V.332