All, thanks for the replies. I am in the process of updating the drivers on my audiobox, which were quite old, doing every windows update, and I've also uninstalled Sonar. When all these things are done, I will reinstall Sonar, turn off Windows sounds, and attempt it in ASIO mode. I also found a program called ASIO4ALL which I may consider running if necessary. When all this is done, I'll come back and give an update.
 
Even though I liked the convenience of running the software with no interface, it may well have made things unstable. Here's to hoping that was all it was.

"I also found a program called ASIO4ALL which I may consider running if necessary"
 
Don't do that. ASIO4All is just a wrapper for the WDM driver to make it look like an ASIO driver to Windows. The Presonus ASIO driver will perform much better, and true ASIO drivers won't work when ASIO4All is installed.
If you haven't downloaded ASIO4All yet, don't. You'll just end up having to remove it to get the Presonus driver to work.

Avoid ASIO4ALL if at all possible. If the Audiobox has its' own drivers use them in preference. ASIO4ALL is a work-around that attempts to compensate for the lack of a manufacturer's ASIO driver for on-board cards such as the Realtek. It works well for some people but can be very difficult to configure and often causes as many problems as it can solve. It also seems to conflict with other ASIO drivers at times and can be very difficult to remove.

One thing might be worth checking in Sonar. The master bus should be set to output to the audio interface, and the hardware has a bus-like meter/volume section in Sonar. Check where the volume slider on that is set and that routing is correct.

Go into Windows control panel/sound and disable all system sounds. Then ensure the Window's volume control isn't set too low. Also, if you only have the one sound card installed, check that the Windows default sound card settings are not only pointing at it but are pointing at the right ins and outs. Any incorrect settings here can cause problems. In Sonar's preferences try ticking the "share audio drivers with other programs" box, or unticking it if it is ticked. It might be that while you are using Sonar Windows seizes control of the sound card for its own purposes and resets the volume/bit depth/sample rate then Sonar fails to reset them to suit Sonar once Windows releases the driver, or vice versa. Another possibility is that Windows is pointed at one set of ins/outs on the card and Donar at another. If these are set to different volumes in the Windows sound mixer, again possible problems.

As for drivers, you need if at all possible to be using drivers that match the version of Windows you are using. Win 8 drivers and some Win 7 will generally work on 8.1, though maybe not optimally. Go further back than Win7 and all bets are off.