Ehhh I don't find that train of thought very convincing. Saying it's Selebus' direct voice simply because you think you ruled out the other options you thought of isn't all that strong an argument.
I think it's more likely we simply don't have the information to accurately parse a lot of that.
Let's go from that then (and I don't mean to be condescending, it is genuine interest). Let me assume that you concede I have effectively ruled out the options I could think of, and let's assume for the sake of argument that it is not, in fact, Selebus' voice. Can you offer a plausible alternative I did not bring up?
I'm willing to concede that I may not have picked up on what Selebus actually meant the extraneous voices to be; I've mentioned before that I'm not the best when it comes to abstract symbology. But then, if no other plausible alternatives can be derived from what we already know, what we're left with is either 1) an error in argument or 2) an error in story-telling.
1) The extraneous voices are meant to explore philosophical or religious themes. In this case, if no plausible premise can be found, Selebus can be assumed to be making arguments without telling us his premise. If we don't have the premise, the arguments are just ramblings without meaning, and to say that "we don't have the information yet" is no excuse, since for an argument to depend on a premise that is granted only so late into the discourse is just an insult to the audience.
2) The extraneous voices are a plot device for the story. In this case, there not being a plausible alternative again means that Selebus is expecting us to show interest in something solely for the fancy wordplay of it, rather than for what it might imply to the story. Again, that just ends up as rambling. The only way to do this effectively would be to give us viable red herrings to keep our interest and allow for a stronger plot twist when he does reveal it later.
Again, I'm willing to grant that I just blatantly missed some obvious cues to plausible alternative explanations. But should that not be the case, the argument that we don't currently have enough information doesn't hold up against the quality of his writing elsewhere, or against the basic expectations an audience can have towards a story-teller. The sorry excuses for philosophical musings that Sensei will sometimes have just don't hold even close to the same level of quality as the rest of the story-telling, and just don't seem to be things you might reasonably expect from a person in his circumstance, especially given, as I mentioned before, how inconsistent they are depending on which character he is dealing with. It's almost like Sensei is just molding into a different character over which to develop each of the female characters, which are the ones given a legitimate level of depth.