The DX-7 is a good radio and you will be happy with it. The servos are compatable, the big problem is the connector. Futaba has the blade on the side of the plug that you will need to carefully remove with an xacto blade, or resolder in all new servo leads, or get the futaba to standard adapters(last resort). You can see just a few moments of razor blade work is the easiest thing to do. The Hitecs are offered in either Futaba or Std plugs, so you may not need to do connector surgery. Just remember that polarity is most important. The black wire on Futaba is the Gnd as is the Brown wire on Hitec or Jr wires. Place this end of the connector onto the "-" symbol on the Spektrum Rx. All will be good. If you get it backwards, they will not work, just flip them over.

Good Luck, Will