It’s best to think of Memory Palace as an expansion module to the modular video synth system that starts with Visual Cortex as the core module. That’s the intended usage of the design. There are ways to use it standalone (just feed oscillators and audio into the RGB inputs, or get a couple video oscillators like Prismatic Ray as your sources, or use stills) or with monochromatic video sources (Cadet 1+Cadet 3, Vidiot, etc), but to get external video in, you’ll want Visual Cortex or TBC2.
That said, this stuff is meant for experimentation… you can patch your external RGB or YPbPr video source directly in with some adapters. You just won’t be properly DC restored or synchronized. You could have fun experimenting though.
To be clear, we don’t have our format of 1V patchable signals because we’re trying to be proprietary or something – it’s so that you save money and have more expandability in the long run! If every module had external video inputs, they’d all be a lot more expensive.