Raise the signal level a few db... try at least 80db on the meter when measuring and turn the mains off initially. Measure only the sub to start with since that's what we are trying to correct. You may need to raise the volume on your sub itself so that it's a bit hotter than your mains.
Go ahead and make that graph 800 pixels wide too.
Btw... did you get your soundcard working? If you did then please (if you don't mind) see if you can help Ryan in
this thread. I believe he has the same sound card as you. Thanks!