The mains are putting out sound when fed a 20 Hz sine wave tone from REW at low volume with a 250 Hz crossover, that is it. I was surprised they made any sound at all. That's why I made this post. I have not looked into whether the sound they make will cause me any trouble yet, I'm waiting for my family life to give me the opportunity.
To sweep the subs using a signal to the mains, as I can't get ASIO to work with REW.
I'm not going to use Audyssey, I'm going to use a miniDSP, that's why I need to sweep the subs manually.