Trying to get my RD-300 to communicate with my GR-1 guitar synthesizer. Got a midi cable from the GR-1 midi out to the RD-300 midi in. Got a cable from the GR-1 mix out to an amp. I get a electric piano sound no matter what setting the GR-1 is on. An uneducated guess is, I need to change midi channels on the keyboard. However, I don't have a manual for the keyboard. Any suggestions?