It depends what you are trying to do, how do you want to use the Audya?

If you just want to use the Audya to follow the guitar chords then you should be playing the left-hand part, which is by default set to MIDI channel 2 in the Audya, so you set the GR-55 to transmit on MIDI channel 2.

The way I was using the Audya was that I was playing the chords, so that the style was following me, and a friend was playing a second MIDI guitar to play the melody on the right-hand on MIDI channel 1. We used a MIDI merge box so that we could both plug into the Audya's MIDI in.