You can define by jumper if you want to have the "mixed" CV3D/Scandoubleroutput going out of the scandoublermonitorport or the CV3D Monitorport. You can also set is to display RTG-Screen only on the CV3D port and PAL-screens only on the scandoublerport.
There is no way you can feed anythin into the CV3D or the scandoubler unless you are a technican that is able to redesign the card.