We will be implementing an installed Sony EVI-D70 in our auditorium that will give a stage view for our house feed system to our lobby and adjacent rooms. I have everything figured out except one detail. We would like to alternate between the camera feed during the show and a PowerPoint slide show for advertising pre/post show and during intermission. The distribution side of it looks like this: S-video cable for video from camera and audio feed from our LS9 to a TecNec RF modulator. It's then standard F-type coax from the modulator to our school's distro rack. My question, what would be the best and/or cheapest (if not one in the same) options for switching between the two sources (video/computer)? Would it be some selector before the modulator or something else? Thanks for the suggestions.