From the basic tenets we can see that the stuff gives rise to at least two realities:
The first is our perceived physical reality which is a result of chains of interactions of patterns of stuff that end with the phenomenon of awareness. This enables us to create an observable and measurable reality of the physical universe. It is this reality that is described and predicted using physics.
The objective reality is the true nature of the stuff. As we interact with it and our perception is born of it we can only infer its nature. From this it is in fact impossible to understand the nature of the stuff because everything in the perceived universe is interaction of the stuff and not the stuff itself.
It may be that the stuff itself is a computational system, or like Max Tegmark suggests a pure mathematical object, or something that we cannot conceive of. The point is that it is a question that cannot be answered. Not quite true. If the stuff were a constructed computation then may be the little green programmers could contact us and let us know.