We have unfortunately not been able to get sufficient feedback to verify the possibilities for all Rivera Amp models.
The footswitches used for the various amp models are (according to the Rivera web-site):
The FS-8, FS-5 and the FS-6 has momentary functions for the channel switching (according to our information). The G-Major can unfortunately not send momentary pulses hence it cannot be used to switch channels on the amplifiers using these footswitches.
FS-7: We have attached a drawing below showing cables which should make it possible to switch between channels and one boost mode.
This has been successfully tested.
Please note that most of the Rivera Amps has more functions than can be controlled by the two relays of the G-Major.
We have been informed that Rivera can offer a MIDI Interface.
Or you can have a look on the Axess Electronics CFX4.
We would like to hear from you, should you find another solution to controlling these amps via MIDI.