Steve,
If a working version of DX is all you want, that is easy. I have one. 3.5. Got it thru Impulse.
Uninstall DX. Turn off betas in Impulse. Restart Impulse, you should see DX 3.5 available. Make sure you haven't hidden apps not installed. Get DX 3.5, voila! Worked for me!
If you have DX Pro, you'll see DesktopX, and DesktopX Pro listed as installed in Impy. Run the one that don't say Pro. You'll see that it still runs the pro version. If I run the Pro, I get an error saying it isn't compatible with my PC.