Finally I have my Pod X3 Live working on Catalina :)
Uninstall exisiting driver using the Line 6 Driver Uninstaller app, then:
Launch the Terminal application and type the following commands at the prompt:
sudo pkgutil --forget com.line6.driver.xtaudio.package
sudo pkgutil --forget com.line6.driver.xtmidi.package
Then
Reboot mac
Disconnect the X3 live (I think this may be crucial as I went through the process without doing this and it did not work)
Install the latest driver (7.6.8)
Reboot mac
Opened the driver config screen via system preferences
Reconnected the X3 and there it is.
Can now use Garage Band etc.