How can you be so confident that no magic is involved in this "how it feels from the inside" business, while casually talking about configurations of neurons?

I usually find Occam's Razor to be sufficient. You are misapplying reductionism: if consciousness maps to a set of configurations of neurons, and neurons map to quarks, spacetime, and probability amplitudes, then we have no need of mysteriously specific exceptions to physical laws. Indeed, such hypothetical and entirely unsupported exceptions have no explanatory power at all.

What's the set of configurations of quarks which feels from the inside like thinking or like the color red?

Why, the set of configurations of quarks which describe any member of the set of neurons which feel from the inside like thinking or like the color red, of course.