Thanks for the responses.
I'm actually finding the starlight one to do quite a good job of explaining how the space elves work, since they're having to explain things to the locals a lot. And like, I don't have the time to go back and read all the stuff any time soon (which, for me, would involve first actually reading the Silmaril? And maybe watching Star Trek?), so I'm just gonna be like 'okay, so they're rationalist space elves from a magic-fuelled post-death utopia/the exact opposite of the Warhammer 40k Universe'. I feel like that about covers it for the purposes of this story.