Hi James,

I looked at your AI file.

Let's try another DXF conversion way.

But at first you need to remove all special effects from the objects in your AI file using Illustrator: I noticed that for some reason straight lines with rounded corners in your AI file have  Grain effect assigned:

1/ You have to remove this effect with Trash button. Then save AI file.

2/ Now in Finder change extension of your AI file from .ai to .pdf

3/ Launch AutoCAD and use menu File -> Import to import file you renamed in step #2

4/ Use standard settings in "Import PDF" dialog:

After importing PDF to AutoCAD you can save it to DWG and to DXF format. Just make scale adjustments with SCALE command.

I attached resulting DWG and DXF files I created in such a way for reference.