Nice feature except it doesn't work as documented.  The documentation says:  SONAR automatically re-routes any Output and Input controls that were assigned to the old synth.  When I replaced Dimension Pro with Rapture, the output track was routed to the Master bus rather than to the bus where I had routed Dimension Pro.

I just tried to duplicate your problem; however, when I replaced Dimension with Rapture it correctly routed it to the same bus, and when I replaced Rapture with Dimension it also correctly routed it to the correct bus.  BTW, I set up multiple sub-buses and tried it several times, but no problems here.

I'm probably having the problem because Sonar is confused about the routing on this project to begin with.  Every time I open the project, Sonar warns me I'm routing to a silent output which I've verified several times is definitely not true.

Same here. It may be my laptop but there's a whole lot of bizzar behavior going on with X2.
 
I just switched to Track View and all but the 1st track was gone - BLACK screen where 20 tracks should have been.
Latency is also different each time I open X2. It's proving to be very buggy on this computer.
 
I have yet to install X2 on my XP desktop system but am going to try it soon to see if these bugs still happen.
 
 
Steve