MuseScore & GarageBand

That's kind of up to you; I still don't understand your question really. If you already have a recording in GarageBand, there really isn't anything MuseScore can do with do with it - MuseScore doesn't operate on audio files. If you can convince GarageBand to general a MusicXML file containing the sheet music , you could load that into MuseScore to display/print the same sheet music but far more professionally engraved. It can also playback the music with some pretty sophisticated sounds, although to be sure it will be different sounds. but that's assuming what you have in GarageBand is all notated music, no actual recorded sounds, as those certainly won't make it into the MusicXML.

In any case, there really would have been no need for GarageBand - you could have entered the music directly into MuseScore and gotten better results more quickly. So in this sense, MuseScore would be more about replacing GarageBand than enhancing it.

Conversely, if you have music in MuseScore, you could export that to MusicXML (or MIDI) and load that into GarageBand, if you want to replace MuseScore's engraving and playback with GarageBand's.

You could also choose to use GarageBand's playback but MuseScore's engraving.

not sure if that's what you're asking, but maybe it helps?