I found this a while ago and have used this to precisely integrate L+R subs in my system. It has allowed me to finally optimize my two channel environment. All I need to do now is place a lock around the controls so I do not fiddle with the integration in the future.
I saved the files and burned them to a CD. The web page provides an explanation of the tests and what to listen for.
The three tests OVER, LATERAL and BEHIND also pan between L+R. The transition should be smooth between the speakers. The tone should not jump between speakers nor sound different at the center referenced from your listening position. If it does, try moving your speakers closer together.
There are other tests on the site. I haven't tried any of these yet.
Edit: The "?" in the title should have been a "TM". I cannot edit the title.