Rhebeqah wrote:
Was rewatching "Angel" and I realised summat. The Oracles that Angel occasionally consults are almost exactly like the Transmundanes. Am I right, Ghul?
I actually created the Transmundane(s), in the thread below in fact:
https://hyperborea.boardhost.com/viewtopic.php?id=326
So I can give you a definitive answer. The original inspiration for the appearance of the Transmundane was the Axons from the classic Doctor Who serial "The Claws of Axos", although the Axons weren't very much like the Transmundane otherwise (if I understood this cannabis-fueled story correctly - which is far from certain - they were actually a facade created by a blob monster for... some reason, plus the Master was involved somehow; like I said, it was pretty clearly cannabis-fueled).
At that point I connected the appearance of the Axons with the Classical imagery seen in a lot of Lovecraft's non-Cthulhu Mythos stories ("Hypnos", "The Tree") and also with the gods of the Dreamlands to create a race of living Greek statues. I made them arrogant and contemptuous of mankind because that frankly seemed more interesting than nice. I made them (generally) evil, but in a way that sometimes benefits mankind (through no particular intention of the Transmundane to do so), because again that seemed more interesting. That was the genesis of the Transmundane (hey, that also sounds like a Doctor Who title).
However, as you have correctly guessed, I am a fan of Buffy and Angel. At some point before writing up the revised text for the hardcover, I remembered the Oracles from the first season of Angel, which did indeed look a lot like the Transmundane. So I slipped in the line about the female being more sympathetic than the male as a mini-homage.
So the Transmundane were actually created as a melange of different ideas, but I did put in a reference to the Oracles on Angel. Congratulations! You are the first person to catch it. Now we'll see if anyone ever decodes "Ka-Ven"... 
