Here's how to set the MIDI channel that will be transmitted when using the Guitar To MIDI feature in the GR-55: 

1. Press EDIT.

2. Press the  PAGE right button to the select the SYSTEM tab.

3. Press the Left or Right cursor button to highlight "MIDI/USB," and then press ENTER.

4. Press the PAGE left or button to select  the GTR-MIDI tab.

5. Press the cursor down button to highlight "STRING CHANNEL."

6. Turn the dial clockwise to choose the desired channel (1-11)

7. Press EXIT when you're finished—the new setting is saved automatically.