gi20/gk3 not controlling moog voyager properly

Hi i'm atempting to use a roland GI20 midi interface & GK3 midi pickup to control my voyager 3.2 (using a guitar) the pickup has a 3 position sw. midi, midi/guitar, guitar only. It works on midi only midi/guitar mix but still plays the moog on guitar only, also the midi volume control is inefective. I've elimiated possible faulty hardware (the roland system has been totally changed, still the same result) both the roland units will play a korg, yamaha or roland synth right out of the box with no alterations to the parameters. I have virtually no midi experience and i'm not to sure how knowlegeable the staff at the shop are.
HELP