Yeah...An Avia disc and an SPL meter would sure help me too

What I've been doing, and it works fairly well, silly as it sounds, is use a CD piece that I have that has guitars running up and down the scales from at least 3, 4 hundred down to well, well into the low bass region.

Ok....so I don't really know what I've got, numbers wise, but at least I know I don't have any gaping holes or lofty peaks in my subs output

And it actually mates well with the rest of the system and sounds good too