There is a wild solution to the cross brands, cross frequency buddy boxes in the Jan issue of RC Model World. It is a device that requires two RX's in the plane and it selects which RXto follow. Check this out. http://www.2icrc.com/

It looks like a lot of work and while it works, it isn't a good option. Futaba has a "wireless link between TX's. I don't know much about it as to whether it may work cross brands.

When Iwas on the Buddy Box, Isupplied both the master and trainer boxes. The Master was a Futaba 9C adn the trainer was an old Futaba Attack 4 channel. It worked verly well with one exception, the throttle trim was an issue and if it was adjusted for idle and cutoff, the trainer TX couldn't get full throttle, and if it was adjusted for full throttle, the trainer couldn't get good throttle down for landing. When I tried to buddy box my Sons 6ch Futaba, to the old Attack for the traniner, things got ugly. This is all between like brands. Cross brands may really require something like the 2icrc solution.

Don