hi denis,
Sounds as if garageband is actually mistaking your vs 20 for a midi controller.
which it does have some midi controls,but i think your going to need to set up
the vs 20 in garagebands preferences/audio inputs/driver.
as well as a surface unit.
the vs 20 is basically both as im sure you know.
i hope you have resolved this issue and feel free to send me a message if you need more asst.
Charlie Roy jr.