I HAVE NO IDEA WHY MY ADAPTER that plugs into my s-video out port to allow me to plug directly into the composite in doesn't work.
Sometimes you have to select the option in your video card software so it knows what type of signal to output.
If you don't have the software, you can download it from Nvidia.
If your adapter allows for component video instead of composite, use that.
There is a world of difference.
I'd buy a different video card before spending money on a box to create a low res composite picture.