The DX9 version comes with the DX11 version. If you have installed the game to the default location, use the file manager (folder icon on the task bar) to navigate to C:\Hitech Creations\Aces High III. Once in that folder scroll down to "aceshigh9.exe". Right click, select "more" and then "create desktop icon". Drop that on the desktop and use it to start the game.
This will start the game in DX9 version. Try this and let us know how it works out for you.