Thanks for your patience on this one... looking at the design spec of the ARC PRO, and the sensor circuits in play I have concluded there are two ways forward.
1/ With some relatively simple additional hardware, an approach based on wiring sensors together will become possible. This solution will function with the Magic unofficial ARC app but not the Hornby official ARC app. This is the quickest and easiest route to getting four lane solutions functioning with the ARC PRO.
2/ I am also working on a more advanced four lane solution which adds compatibility with both the Hornby official ARC app and the Magic unofficial ARC app. To get this solution functioning requires some quite advanced firmware to be written and endurance tested. Also, this approach involves a lot more design effort... it will bring some added opportunities... e.g more advanced sensing of vehicles entering pit lanes etc.
I am working on both... clearly 1 will be ready first...
Hope this update helps...