"Aphrodite's child" is totally unknown to me, but "Demis Roussos" is not. My parents had at least 1 album by this guy, maybe more and they played it when I was young.
What I discovered when I started to discover the early birds in electronic music, is that many have a rock background (talking about the 70s), and started to experiment with electronic music in (side/other) projects.
Vangelis: The first open-air concert I've been to, was by Vangelis. The city of Rotterdam arranged this open-air concert right in the middle of the city at the riverside, with the audience at both sides of the river, the bridges connecting both sides, and on the little island in between the two riverbanks. His music was combined with a spectacular light show. Such a massive goosebump event! Not sure what year exactly this was, but must have been the late 80s, maybe early 90s. "Blade Runner"; I have that album somewhere, on CD.