Thank you for the advice. One problem is resolved, but another has popped up.
First of all, I was mistaken in my comment above when I said the spline appeared to be smooth in Carbide Create. I took a look at the file again and the spline actually did become faceted when the DXF file was imported into Carbide Create. Here is a screen shot of Carbide Create with a direct import of my DXF file. Note the faceting of the spline that is most apparent on tight bends:
I imported the same DXF file into Inkscape and the spline is smooth as it was in the CAD program in which it was created:
From Inkscape I saved the geometry as an SVG file which I then opened in Carbide Create. The spline now looks perfectly smooth, however for some reason all of the straight lines have disappeared. The spline and arcs are present, but there are no line elements. In Inkscape there are several different options for saving SVG files (Inkscape SVG, Plain SVG, Optimized SVG). I tried saving each type and they all result in the same output:
As a check of the file's integrity, I imported the same SVG file into MakerCam and the spline, arcs, and line segments are all intact (the centerlines are missing, but that is probably because they were created as draft entities rather than true line geometry elements) :
Even though DXF and SVG are supposed to be neutral file formats, its apparent that each program looks at them in a different way. I'll keep playing around with various ways of importing and exporting the files and hopefully come up with a combination that brings all of the geometry into Carbide Create.