Dui, ni shuo de dui
None of these methods are really great because you have to select each time which slice you want to export.
It would be nice to have a tool who could do it for the whole design.
For instance, just select a face view (top, front, right, whatever), then what you see on the screen is what you get as a DXF, it just has to export the same lines.
I have no idea how complex this operation would be to code, but the manual “DIY” way would be to make a screenshot, then use a vectoring tool to convert into a SVG of DXF file.
Too bad it doesn’t seem to exist, it is quite a pain to do several slicings every time.