This is a toally wide curve ball I'm throwing here.... and it could be a bit of a stretch, so open your minds a lil...
Using your theory, the theory of Angiens and what we know of Shades.... the shades mimic (mirror if you will) our world... The seek peace when we do, they war when we war....
Is it remotely possible the Shades and the Angiens are the same beings... just different 'reflections' if you will?
Angiens reflecting all that is bright and 'good' to an extent, and Shades reflecting all that is dark and 'not-so-good'?
I know its a stretch, but it would tie a lot of theories together...
<---Take my Avi as example.... Bright and Fiery on one half.... Dark and mysterious on the other, but all the same being. It is the nature of us all isnt it?