The 4 channel JR radio will work as the slave unit with out any problems. just plug in the DSC lead in the back of both transmitter with the Master(X9303) swithced on. You will have to go into the settings of the X9303 and set the trainer set up on. All that is being used in the slave unit is the encoder(sticks) section of the unit. The channel 6 is used from the master unit not the slave unit.

Hope this helps

Cheers