Keep in mind that he recently commented on being underwhelmed by the lackluster performance of his new sub. I'd venture to guess that phase may be the culprit.
This is why using a test disc is ideal. You can play the 80Hz track and it will be played through both front mains and the sub. And also why you'd want to disconnect the other speaker.
Do you own any of these?
Something else that's important to note: I seem to remember reading that your current setup is temporary, as in you just placed your sub somewhere up front to demo it when it first arrived. If that's the case, and later on you move it to another location, you'll change its phase relationship in doing so and will need to adjust it again. So maybe now is a really good time to find its permanent home.