You could always make your own rgb to svideo converter
http://www.nexusuk.org/projects/rgb2svid/It seems pretty basic electronik but the hard part is getting hold of a CXA1645 IC i think they dont make them anymore.
But apparantly that circuit is standart on the PSX (if you have a spare or broken PSX), so you could salvage that chip and use it. Or you could leave the chip in the PSX motherboard and solder the Amiga RGB signal directly to the chip and break the RGB signal from the PSX to the chip. So the pin output from the PSX gives you the Amiga picture.
