You could try using the actors that have the option to ignore their connected processes when a 'gated' parameter is enabled. These are the'Selector' and 'Router' actors. The Isadora manual explains these in more detail.
Perhaps begin with an easier example, here are so many different and complicate propositions…
corrections: kinect V1 work with processing 2 and 3, it's the SimpleOpenNi library for skeleton who works only with processing 2 at the moment (there is a improved version for P3 on github, but it doesn't work for me). All V2 model are working but you need the "kinect adaptor" from Microsoft to use it and an USB3 plug.
You can try hard masking the projector lens. I have used many times removable self adhesive vinyl to physically soften the projection frame. It is the same vinyl used for vinyl cut lettering etc. used in galleries and signwriting. The adhesive is not applied directly to your projector lens, but onto the projector or lens casing so that the vinyl is suspended just off the glass. It is also a way to blend overlapping projectors on the fly without using software blending. I did design a shutter and iris to go at the front of the projector lens for just this purpose but never got around to building them so I am still using the vinyl solution!
@jhoepffner Thank you for the info. We will keep exploring the set up we have achieved for now at least with the two channels and see where this takes us . If you develop the Max patch and happy to share would be interested in seeing it how it works. Thanks again. Lucie