Hi Bill,
I've printed some things with S3D on my CubeX (single). I'm getting pretty good results, but S3D doesn't directly support BFB-style gcode with inline M108 commands to control flow rate and M227/M228 commands to control retraction. This means that for some parts where you want the feed rate and flow rate to change (e.g., ones with layers that have small surface area or for thinner support), to get good results you have to manually insert these commands inline in the gcode.
I was thinking of writing a post-processing script to try to automate this, but right now I'm playing with the new version of Cura since, like Kisslicer, it has built-in support for BFB-style gcode and it seems like a nice extensible platform (e.g., modular architecture with python plugins and json settings files). I created a CubeX printer profile for it and a very simple Python post-processing script and I'm trying to dial in the settings to get better prints.
I'm no 3D printing expert, but I will say that I'm having much better slicing results with S3D than with Kisslicer or Cura. Maybe I'll go ahead and write a simple post-processing script for S3D that inserts M108 commands as the feed rate changes. I don't yet understand how to optimize retraction settings (M227/M228), so I will have to study Kisslicer and Cubitmod to get a better idea of what's going on there if I'm going to try to adapt these to S3D.
Another thought is to swap out the controller with open hardware/firmware, as others have done. It seems like the result would be a better and more extensible printer.
Michael