Well, I will continue anyhow as maybe this will help someone.
Being unsure if the via epia 5000 mini-itx motherboard supports composite sync (I am still unsure), I build the 'separate sync to composite sync adapter' described here: http://www.tkk.fi/Misc/Electronics/c.../vga2rgbs.html
The epia 5000 apparently does not provide 5 volts from pin 9 of the vga port, so I had to run a separate line.
The sync adapter, as you can see in the picture, did not fix the dual screen problem, but something (maybe the adapter) made the colors more accurate from the last wiring scheme. Plus it seems more stable.
The picture is just Xwindows running with a generic 640x480 xorg.conf
I think the double screen has to do with my continued inability to set up Xwindows to run the screen at the correct frequency.