When I use Addictive Drums the drums stops playing immediately when I hit the space bar. Is there a way to make EZD to behave the same way? It's a bit annoying having to stop and start the two sound engines separately.

what do you mean?
And how would sonar know when do you want this to happen?

OK, the situation is this: I have a guitar track recorded in Sonar and I want to find a nice groove in EZD. I play the guitar track in Sonar and listen to various drum beats in EZD. Then, when I stop playing the guitar track in Sonar (hitting the space bar, clicking on the "stop", "pause" button or whatever) EZ-drummer keeps on playing the midi loop as I am not being able to controll this from Sonar provided I haven't draggd the midi file to EZD:s midi track. I want EZD to behave the same way Addictive Drums do, which is synchronized to the host's controllers. "Stop" and "play" of the loop is only controlled by the midi-player in EZD? Hope I am expressing myself clear enough?

I don't think you can do that.
I guess this would have to be implemented by toontrack to make EZD follow Sonar's transport buttons. 
Maybe an on/off button for this...otherwise EZD would start when you already have the loops in the track view and then you would have 2 drums playing on top of each other.
Maybe someone has a workaround.

I see... Thanks djoni!