Sonar X1, unwanted audio silencing, and multi-tasking in Windows 7

Sonar X1 is great. My only problem with it might just be a Windows 7 issue I'm not sure. My problem is that when I use Sonar X1 in conjunction with Reason in Rewire mode, when I switch to Reason the audio suddenly silences and I can't hear anything unless I switch back to Sonar. This is a problem because when I'm trying to cycle through sounds in Reason to test I can't hear anything unless I'm in Sonar which just takes an extremely long time to keep switching back and forth just so I can hear what's happening. I've tried fiddling around with the volume control settings and playback device properties (the "Allow applications to take exclusive control of this device" checkbox etc) but nothing seems to help. Is this a feature of Sonar or Windows 7? I never had this problem in WinXP. In fact, I miss WinXP's simple and straight-forward mixer controls with their direct access to sound device inputs and outputs.

Any ideas? Am I explaining this well?

EDIT: I just realized that when Sonar is not playing and you switch tasks the audio engine stops which is the cause of the problem. Is there anyway to keep it going while multi-tasking?

Thanks for the reply. But like I said, I'm running Reason in Rewire under Sonar so the audio driver options are all greyed out because it's running through Sonar's audio engine, and therefore Sonar's driver settings. But when I alt-tab to Reason the audio engine in Sonar shuts off so I can't hear anything. And I already have "Share drivers with other programs" checked, not that it matters because it IS using Sonar's drivers and doesn't need to be shared. It works fine multi-tasking during playback, but when playback is stopped the audio engine turns itself off when alt-tabbing to Reason.