> Qualia exist "outside" spacetime, e.g. redness doesn't have a position in spacetime.

I'm sensing redness here and now, so the sensation of redness exists very clearly tied to a particular point in spacetime. In what sense is the qualia of redness not firmly anchored in spacetime? Of course, you could talk about the concept redness, like the concept Pi, but even then, these concepts exist in the mind of a human thinking about them, still tied to a particular location in spacetime.

> If consciousness is purely physical, then how can two identical systems (identical brains with identical sensory input) giving rise by definition to the same qualia not literally be the same consciousness?

The two brains don't receive the same sensory inputs, nothing in the experiment says they do. From the second right after the duplicate is created, their sensory inputs diverge, and so they become separate consciousnesses with the same history. They are interchangeable initially, if you gave the same sensory inputs to either of them, they would have the same output (even internally). But, they are not identical: giving some sensory input to one of them will not create any effect directly in the other one.