GarageBand is a popular and simple tool for OS X/iOS users to produce music. Being a free program, it's no wonder people turn to GarageBand for all their musical needs. However, can you use GarageBand to run tracks?
GarageBand was made to create within the app and deliver a stereo mix. There is no multiple-output routing. You can run your Auto-Panned mix, provided in the zip file we deliver, or you can run the accompaniment track in stereo without click or guide.
One thing GaragageBand is great for is editing arrangements. As shown in the Editing an arrangement video, you can input the tempo and time signature into GarageBand, move and duplicate sections, and export a stereo mix of your arrangement.
From there I'd advise finding a different solution for playback, like perhaps our app for iOS devices Playback!