Drago keep just one engine in "Game engine" settings. For using other engine people have to change the path, binary and parameters every time. If Drago can retain more than one GTP engine settings, that would be much more convenient for sellecting between different engines, and enable engine vs engine.
[content with image inlined deleted]
I did not want the image inlined but I was unable to edit the answer because the thread has desappeared from the forum page...
This is exactly the goal of the version under development! You can have a look to the "New game engine" dialog with time settings and engine selection at http://www.godrago.net/Images/NewEngineGame.png.