s400 is firewire, 4 pin
so, digital optical or firewire?
are you trying to play it off the camera?
the audio quality should be dictated by the camera (assuming s400 = canon powershot s400)
the firewire would just be a transfer to get it off the camera and play through the computer…
more info?
Seeing as they are both digital you probably will not notice little difference between the two.