Hurrah! As it happens last thing yesterday I grabbed the latest, latest beta Armbian & lo & behold, I got a composite picture on my screen from it. Excellent stuff! Would copying some of the Fex settings to an Orange Pi One image (say, RetrOrangePi as I noticed that has a specific image for it) work or are they too different?
Got my (512mb) Orange Pi Zero a few days ago & have tried booting it with both an Orange Pi PC RetrOrangePi (latest) distro & a beta Armbian distro specifically for the Zero; both have booted & I've succeeded in logging in over SSH via Ethernet so I know it works. CVBS / composite video doesn't seem to be enabled by default on it, however. Might be an idea.