I dislike the built-in metronome sound in Mainstage, but until last week I didn’t realize there was a way to change it. After doing some hunting, I discovered a way to get a much better metronome sound.
1. Open Mainstage. Select a template.
2. Under the channel strip window, select “Show metronome channel strip”.
3. This channel strip should now be visible.
4. Select the Ultrabeat plugin instead of the Klopgeist.
5. Select “Percussion Bank”.
6. If you’d like to change the metronome sound, select “block” and then change the sample at the bottom of the plugin window.