This reminds me of an issue I had with getting sound from both Sonar and Windows using my dedicated audio interface.
It seemed to just work by default if I let Sonar run at 44.1/16. That is the default Windows sound format as far as I can tell. The audio interface allowed anything, including Sonar, media players, browsers, etc., running on the PC to play over my monitors.
But if I changed the sampling rate of my audio drivers through Sonar, suddenly no more Windows sounds!
Then I found this little trick. Go to Windows Sound > Playback Devices > Select your Line 1/2 output (or whatever you are using) > Properties > Advanced > Adjust the default format to what Sonar and your audio interface are now set at.
Boom! Both Sonar and Windows can use the same audio output again
Interface drivers may differ, so YMMV.