If you have a REX receiver, you can test whether it works via the E1 and E2 ports set as EX-bus.
In the REX receiver, these ports work as expander, so it is not certain that it works.
Yes this works, tested with REX 10 but its too big to fit into fuselage , R9 fits thight. Best would be a "REX9" but this is not existing. REX7 I miss one channel (F5J) .