I'm not sure if a entry is needed in that DLL.xml. Thought I read that somewhere, for that DLL.xml: C:\Users\xxxx\AppData\Roaming\Lockheed Martin\Prepar3D v2
Yes, that's the correct folder, and you must surely have a line for the Addon Manager in it ( bglmanx.dll ), otherwise nothing will work, and you will not have any FSDT menus ( Addon Manager, Couatl, GSX, etc. )
Couatl.exe, being an .exe, is instead called from EXE.XML