Hi 3image, it looks like it's just how those viewer programs draw general spline curves, it's not unusual for AutoCAD to draw all curves as a series of line segments, there may be an option in the viewer somewhere for the density of lines to use.

Can you also send the DXF file that Rhino exported so I can take a look at why that's working better for your case here? My best guess is that Rhino exports these curves as a polyline entity that has arcs in it, either that or it creates individual line and arc objects, and your viewer program draws arcs in a better way than it draws general spline curve entities.

If you use Edit > Separate inside of MoI to break that long joined curve apart into individual lines and arcs, that will probably work better for you since then MoI will also create LINE and ARC entities for those rather than making a single longer general SPLINE entity.

- Michael