Well, here is a super short attempt at answering your question. Jakes' post is right. But, in short, get (1) SPL meter, (2) RCA splitter to divide SPL single out to two ch, (3) soundcard with RCA or Digital out. I did optic to AVR with Radio Shack digital SPL. (Used Behringer U-control ACA202).

After that, just calibrate the soundcard, then test the room with the sub level only - if that is all you want. Sadly, you have to play with it. It is a fantastic program for free. For $100 I would have many complaints. Play with it and you will get the basics. I'm not past the basics, so after that, let me know.

Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire