So you want to be able to see the OrangeRX RSSI?
The way i did it was by building a buffer circuit and feed that into A0 on the APM. MinimOSD picks up the RX RSSI through the mavlink messages (tuning required).
I read in a few places that you need a time constant of greater than 27ms, using this tool you should be able to find a combination that works for you.
Once you have build the filter connect it up between the RSSI S pin on the RX, ground and the A0 pin on the APM. If you have done it right there should be no smoke.
Hook up the APM to mission planer and navigate to Config /Tuning Standard Params and Change Receiver RSSI Sensing Pin to A0, write parameters and disconnect.
You should now have working RX analog RSSI on the APM and MinimOSD, which will need to be tuned for you min and max.