I'm still thinking that a capture card is the best way to go; uncompressed 4:2:2 is the minimum requirements.
I'm following an Aja Kona/Xena LHe, but as it's PCI-E, and I have only one PCI-E occupied by the video card, I should find a PCI video card if I want to install the Aja card... anyone has experience with an Aja capture card that has composite input?