Well, THAT was informative…
I spent some time playing with Luban. It is not the latest version, as my Linux distro on my laptop is not up-to-date, and versions of Luban later than 4.6 won’t work. So, there’s that.
Luban seems to generate G-code well enough, but I cannot find a way to insert custom starting and ending gcodes, as I can with Cura. As discussed in this thread, some massaging of the gcode is necessary to get IDEX to work correctly when gcode is fed in thru USB-B. I suppose I could put the custom gcodes in Octoprint to get around this.
I also looked at using Luban without Octoprint. No go. I can upload the gcode to the printer over Wifi, but have to go to the printer and use the touchscreen to start printing. My printer and laptop are far apart, so that’s a deal breaker. There seems to be a way to print the gcode directly from Luban, but the code keeps stopping, without telling me why. Perhaps it is feuding with Octoprint? I use Octoprint to watch the printing on video, and to control the lights. Again, it appears that Snapmaker doesn’t like letting USB-B control the print. I have yet to try unplugging USB-B, and seeing if Luban works better that way.
It is disappointing that Snapmaker no longer supports the open source version of its IDEX firmware on github. So, I will continue with my current workflow for now: slice with Cura, upload gcode to Octoprint, and print from there over USB-B.