What we have done is bought the wireless interface RF-X which Sussex Model Centre suggested. We have plugged it into the USB and attempted the binding process, but it did not work. The controller shows the orange light on which I believe means it is transmitting? On the wireless interface it has a red light which is flashing, if it successfully binds than it will go a solid red.
Sorry, I should've read the post carefully. You are using a wireless interface ,not a hard wired lead. Not sure on this one but if the interface is transmitting then you need to go into the DX8 bind mode as if you were binding (pairing) a receiver.
Note: Interface is not compatible with version 6 or lower.
Oh, and ensure you are PPM mode on the Transmitter.
DX8 owners jump in here....
Edit: Have you selected from the Real flight menu Simulation (top left corner) and chose the transmitter you are using. That is a definitely a good start.