So, I'd heard this theory before...but I never really understood it. I would like to hear the thoughts of wiser heads, and especially in regards to how much basis it has.

Some background, as I understand it.

Daedra are the blood of Sithis.

Stars are the blood of Anu.

Aedra are both, thus their capacity for good or evil.

White Gold Tower can apparently channel Aurbis (or Aetherius?)

The Marukhati Selectives caused a Dragon Break by 'dancing on the Tower' some ambiguity as to the literal meaning of the Tower, whether the ideal or the physical is meant.

My understanding

In Where Were You When The Dragon Broke we learn that, among other things, eight stars fell during the Marukhati Dragon Break. More precisely "all the folk of http://elderscrolls.wikia.com/wiki/Tamriel during the http://elderscrolls.wikia.com/wiki/Dragon_Break in whatever 'when' they were caught in, tracked the fall of the eight stars. And that is how they counted their days.”

The theory goes that these eight falling stars represent the Star-blood, or the original divine sparks being replaced, as the Selectives are now the Divines.

Furthermore, I'm quite certain this is what Mannimarco means when he says "http://elderscrolls.wikia.com/wiki/Marukh showed us all the glories of the Dawn so that we might learn, simply: as above, so below.”

That is, eight gods before, eight gods after. But the nature of those gods can change. Which is what the Selectives did. They mantled the gods, and so even in becoming them they changed them from Mer-like ancestor spirits to something less Merrish.

Follow on questions:

Assuming this happened, why were there eight stars and not seven, assuming Auriel mantled Aka?

My best answer would be that the whole of the former Aka-Aedra was rejected, but I'm not sure if this is right.

I also don't really understand how Mannimarco became God of Worms using this method, as far as I see there was no god for him to be, or mantle.

But, then again, is that why he was cast down (or able to be cast down by the Jills) from being the God of Worms? Because he wasn't mantling anything?

Can't really comment on Divines-as -selective (I don't find it particularly enthralling, but that's just me), but as far as Mannimacro goes...time paradox. He simultaneously failed in becoming a god, and actually achieving divinity thanks to the Dragon Break. The Mannimacro we faced in Oblivion is (presumably) the prior, while Mannimacro persists as the God of Worms.

It's mortals that are a combination of both, not all Daedra are padomaic since we know there are a few anuic and there could be padomaic Aedra but a majority are presumed to be anuic. The stars are tears made in the fabric of Mundus to Aetherius made by Magnus and his followers after removing themselves completely from Lorkhan's plan.

Though Akatosh would be padomaic and anuic due to the metaphysical tango Auriel and Shezarr ended up doing to fuse into Akatosh.