Guy,
Once it’s set up, the PSX-AR just does its thing reliably. Getting back to your original question, a single PSX-AR will handle this job.
Although I don’t have Loconet, since I set up my CCTV camera so that it can see the PSX-AR’s LEDs at what would be Switch A in the diagram, I can even monitor it, mainly to confirm I’ve managed to derail something…which is fairly rare, considering it’s HOn3 that’s down a helix underneath the main part of the layout.