This doesn't answer your question, but if it were me, I'd be looking for the right projector/lens for the job.
If you were on Windows, I would suggest an MST Hub. Cheap and cheerful!
What is an MST hub, and how can I tell if it will work in my setup? | Canada (startech.com) Can't speak to the splitters on a MAC.
The extenders will work fine for blending. I have a Matrox QH2G and it works great, but unless you already own all the other gear, there may be other options that are more efficient.