Enchanting Ethereal items

[Addah]

I have an ethereal Guardian runeword and I can't enchant it with anything, but on the other hand I can enchant ethereal runeword weapons, is there any reason why it's setup this way?

I made this ethereal runeword armor with the intention of adding 2 10% dmg reduction enchants, is it possible to either change the system or swap out the item?

Thanks


P.S. Can you tell me if Scroll of Weapon Upgrade works with Superior/Ethereal items? Can it have sockets? Or does it work exactly like the cube formula?