I've have only just figured out why the filament for tool 2 was being retracted after a tool change, the G90 reset E position to absolute so I had to add E83 to the toolchange gcode in the firmware. Now I can finally start the head calibration print 🙂 Will let you know what my findings are after I start my first real DXU print.
I had dual extrusion before btw, but not with a lifting nozzle. It caused the nozzle of tool 2 to regularly hit the print and create scratches.