S-Video and Y/C are one and the same. Y/C is the older term.
The luma(light)and chroma(color) signals are on separete wires in s-video/YC while in composite video they are merged. The 1084 has seperate luma and chroma inputs and on rca jacks and you need this cable to adapt the standard 4 pin mini din plug to it's input. Signal wise, they are identical, it is just a cabling difference.