Hello, for what it's worth, this is how I got my 003 to work with 2018 on High Sierra.
1. Uninstall Avid 003 Family Drivers
2. Uninstall 11 Rack and NEVER reinstall it. Don't let Application Manager install it even if it nags you!
3. Disconnect 003 from computer- not just off but remove firewire cable - it is important not to have the 003 connected during installation
4. Reinstall Pro Tools app - whichever version you use - DO NOT Launch app yet
5. Restart computer
5. Install 003_Family_11.1.5 drivers from:
http://avid.force.com/pkb/articles/d...02-003-Drivers
6. Shut down computer
7. Connect 003 to computer and power on computer
8. Turn on computer
9. Open Avid 003 Family in System Preferences and make sure it is connected and choose settings - Optical Format setting should be ADAT
10. Open Audio Midi Settings and choose 003 for sound in and out
11. Launch Pro Tools
12. Never install 11 Rack Drivers
This worked for me. I hope it helps someone else:)