Just saw your post, sometimes I have restart issues with X2a in Win 7 sp1 (64 bit) but usually only when Sonar crashes, it won't restart again. I then go to task manager and click "end process" and shut down Sonar.exe from there. But then I have to wait for a few minutes until sonar actually stops. I don't usually bother rebooting, it seems to restart fine. Mostly the cause of the crash is a plugin.
But in your case, you should look at your audio drivers, and I'm not sure if you're using ASIO or other drivers, but for me ASIO seems to be the most stable, with my audio card.
The other thing which could cause instability issues is Video card drivers, they can be notorious especially if you're using dual monitors, sometimes things get screwy with that. I found that xray view caused instability issues on my system so I turned it off in Sonar and never had problems with video drivers after that.
In terms of Jbridge I'd avoid it like the plague if it was me, I tried it and had nothing but problems, big crashes all the time. Went back to using bitbridge and those issues stopped. but to be honest I don't use many 32 bit plugins in Sonar 64x, I just find that some 32 bit plugins can cause stability problems in Sonar 64x.
And yes you'll find with bitbridge you can't use all your 32 bit plugins in Sonar 64 bit, they won't appear in plugin manager.
I ended up biting the bullet and condensed my plugins down to the essential ones I use and got 64 bit versions and haven't looked back.