MacOS - High Sierra 10.13.4 - Working - How-to
I was able to get this running but took a combination of instructions in this post and downloading drivers separately.
1. Log into your line6.com account. Download GearBox 3.72 .dmg file
2. Double click on the GearBox 3.72 .dmg file
3. Double click on the Gearbox icon
4. Right-click on the GearBox.mpkg icon
5. Choose Show Package Contents
6. Visit Contents -> Packages
7. Install all of those .pkg files. I had to allow each installation by visiting System Preferences -> Security -> Allow apps
8. Log into line6.com and visit the Downloads page: https://line6.com/software/
9. Choose Products: GuitarPort
10. All software: Drivers
11. Mac OS X for OS
12. Click Go
-- This next step I did but not sure if it helped or not --
13. Download and install "Version 7.6.7"
-- After restart, GearBox loads but does not recognize GuitarPort --
14. Go back to step 8 - 12
-- After downloading and installing the next drivers it worked! --
15. Download and install "Version 7.6.4" "This update adds support for macOS 10.12 Sierra."
-- Afer a restart and opening up GearBox it gave me an error about updating firmware -- I ignored that and it worked! I was able to hear guitar and works in Garageband as well (after telling GarageBand that I wanted my input to be the GuitarPort and my output to be GuitarPort - I then use headphones out of the GuitarPort for monitoring)
Good luck!
