An individual sensation - the finest grain of that texture of sensation you're always experiencing, e.g. some pixel of red in your visual field - is supposed to be the very same thing as a particular massed movement of billions of atoms somewhere in your visual cortex.

No, not the very same thing. Many kinds of "massed movement of billions of atoms" can generate the same sensation. Sure, exactly the same movement of the whole brain will always generate the same sensation, but in real life, it won't just happen, a brain will never be exactly in the same state.

you're still tending towards a type of dualism, property dualism, because you're saying that along with its physically recognizable properties, this flow of atoms has a property that otherwise plays no role in physics, the property of "how it feels".

The configuration of atoms on my hard disk has a property of being an ext4 filesystem, while being an ext4 filesystem plays no role in physics, so I believe in property dualism ? Property is part of the map, not of the territory. The property of that hard disk is that it holds that movie file. The same movie file (for me, at the level of the map which is useful to me) exists on my USB key, and on that DVD. The physical configuration of the two is totally different, for me it's the same file.

It's exactly the same with "feeling" or "seeing red". And it doesn't matter that my DVD is slightly damaged so some DVD players will be able to read it, but others won't, making it a "borderline case".

But you can't reduce the mind itself in this way, because of the circularity involved.

I don't see the problem with that kind of circularity (but maybe I did read too much Hoftsdatder, so "strange loops" have became a normal fundamental concept to me). Also, you seem to forget that perception involve vagueness. Our perceptions aren't binary "red" and "orange". When require to classify something between "red" and "orange", we'll end up with one (one will get slightly higher activation), but overall, the "red" or "orange" symbols in our brain are more-or-less strongly activated and can be activated at the same time for borderline cases. So the borderline cases aren't even that problematic.