I have a Taz 5 with the Dual Extruder V2 and I am not able to merge print. In software I am able to merge the 2 .stl files so it looks correct on the screen but when I print it will only use one extruder and not show the merged print on the print bed, just as shown before I merged them. Any help would be appreciated.
Dual Extruder printing is controlled primarily by the slicer. It generates the gcode commands to switch extruders, heat and cool the extruders, handle the nozzle offsets, etc. It is possible to pass some of these functions (like nozzle offsets) to the firmware (and of course, the firmware must be dual extruder aware).
With that said, we need to know more about the slicer you are using and perhaps share the .stl files you are trying to print. Details on the steps you used as opposed to your summary might help us help you.