As we know the universe better (e.g., through science, through debate of ideas in a philosophical discussion, etc), we can limit the number of viable conceptual schemes (i.e., restrict 'truth' to something more specific) ...

Actually, a large part of what is achieved by the process you described is in fact agreement on linguistic conventions, not a limitation on conceptual schemes. For one thing, conceptual schemes cannot be directly communicated, so any theoretical discussion must necessarily center on the language we want to use to describe Experience.

... but we still cannot reduce the number of feasible conceptual schemes to one. I think this is why 'truth' is seen differently by so many.

There's one aspect of "truth" which I need you to ignore for now: it's the truth in statements such as "God exists". The reason we can't discuss that for now is that we have not, yet, agreed on a way to describe what "God" is. God is not an Object, Theory, Language, conceptual scheme, or any other word we seem to be agreeing on the meaning.

But I think you're trying to get where I'm trying to get, which is a rational demonstration that what we call the universe is not purely objective. In other words, the universe is an Object plus something else to be defined. I'd venture to say that "the universe" is subjective to a large extent, but I fear you'll be thinking I'm a solipsist, which is not the case. So let's save that discussion for when we have more clear words to use.