I asked a similar question here a while back. I also use CorelDraw X3. I export the cdr file as a dxf like you said. Once I have the dxf, I have to open that dxf in AutoCAD to manually edit the drawing. That's the only way I can get AP100 (Amada Laser cutting software) to generate the NC code. Otherwise my computer locks up because there are too many points in the drawing. The drawing needs to be made up of lines, arcs, circles, etc. not splines which is what CorelDraw seems to do with the dxf.
Sorry I couldn't help you more. I had the same problem. Basically have use AutoCAD to trace the existing dxf.