Ned
This seems to be changing. More and more systems are comming with mics and auto calibration routines built in. The technology is caatching up to address this problem.
Avia, VE, receiver test tones and sine waves will all give different results. Which is "correct" ? None of them. All of them. Perfect subwoofer calibration is not only arbitrary but not even possible (in an untreated room). Try this- get the level just right with whatever noise reference...