I have downloaded the demo version of EZD2 and have been using it in standalone mode only.  I have not opened it in Sonar yet and based on this thread and one in the Toontrack forums I think I will hold off on purchasing it until these issues are resolved. I've restored my computer to a point before I downloaded the EZD2 demo.   I'll keep watching here for word of resolution.
For what it's worth, since getting AD with X3, much of the time I build the basic MIDI drum track with EZDrummer as I like the grooves in that program better for the kind of music I do.  (The new EZD2 interface is really slick for that, too) Then I copy the MIDI track to AD because I like the drum samples and the tools to edit the sounds better in AD.  I built a couple of drum maps to translate between the two and it works pretty well.

EZDrummer 2 and Superior Drummer updated today:
https://www.toontrack.com/forum/forum-announcements/ezdrummer-2-0-1-now-available/
https://www.toontrack.com/forum/forum-announcements/superior-2-4-0-now-available/
 
The list of changes includes several crash fixes related to output buses so hopefully this will help some of you. (And me, once I upgrade to X3 later today.)