I would definitely be interested in finding the solution of this issue and absolutely pleased if you could help me. Leading through my problem. 😊
As I said above:
You would start with a single z axis configuration using the web tool, and then manually add the second driver to the Z axis configuration in M584.
To show you exactly what to change you'd need to share your existing config for the single driver and then tell us which additional driver you want to use.
The tool can only create a basic setup. Adding the second Z driver is quite easy though, we just need to know which drivers you are connected to.
When wiring up the motors, verify the phases first.