that's a pretty damn good tutorial, very nice find!
on another note, it's a bit too precise for most people, and unless you are looking to do some serious competing or are just super anal retentive, it's not really necessary.
Set the levels on the sound card at something reasonable, and then tune the gain on your amp like you would any other system.
If you're unsure about how to do that, check here:
http://www.350z-tech.com/zwiki/Tutor...plifier_Tuning