Hello Andy,
The 2.4GHz transmitters send a coded signal which can only be understood by a matching receiver, you are not able to use other receivers with your Futaba transmitter other than the specified one. Definitely NOT any othe make of receiver.
I have recently bought a new Futabe 6EX-2GHz set which they are now selling with the R607FS rather than the original R606FS receiver. I did check this with my old transmitter and it worked fine. Apart from that you need to ask Ripmax if other receivers are compatible but it is unlikely, in my opinion.
Fred
