@ Musicman65: i don't think that automatic volume leveling implies what you say.
I think that the thought is: two different profiles should have the same volume level if they have the same input settings and the same output level.
If you check some profiles they have huge differences, and this leads to some problems.
Like stated before the problem is "measured loudness vs. perceived loudness". Even if you could do something like analyzing the frequency curve of your guitar input signal and automatically compare the output levels of the rigs and then automatically adjust the rigs output levels, it would gain you nothing. As the low end frquencies will carry most the energy it will tell you nothing about the mid structure of a tone. But it´s the mid frequencies that makes you judge if a tone is louder or softer, even if the measured loudness is the same. The perceived loudness dramatically changes with your monitoring system. If you monitor over a system with massive low end like some decent 3 way main studio monitors that translate low frecuencies very well your results will be totally off compared to some near field monitors with 5 inch woofers.
It is really was all that simple, running some analyzing algorhythms, nobosy would need mastering studios anymore.
If you check some profiles they have huge differences, and this leads to some problems.
Yes, this was what prompted my request in the first place. And as for varying guitar inputs etc., I didn't expect anything so complex. All I was looking for was an internal process (exclusive of any guitar input) that analyzed input/output and did a simple overall volume adjustment. I've had to burn a stomp or fx button on a clean boost quite a few times to get a rig to an even level with the others. To be truthful, I haven't tried to use the volume adjustment for all of them, because they seem so low and I don't want the volume all the way up. Maybe that's what I should do, and maybe it would be sufficient ...
What about the volume in the cab block? 
What about a solution like iTunes "SoundCheck" features, that scans your songs and adjust their volume automatically in regard to your library?
It could be a similar tools somewhere in system/options that adjust the volume in regard of your default settings and "Amp Library"...
Just thinking out loud 
What about the volume in the cab block?
yup +1
Mhhh... I don't think it might work. While you can measure the (maximum) amplitude of an audio file, there's no audio file in the KPA to be measured. And you can't predict the loudness of a "sound generator" like the KPA.
Even using a reference tone, loudness would be different at the various freqs. If I profiled an amp with more gain it has to sound louder. And, even with the same gain & MV settings, if tone controls are lower in a profile it has to sound weaker.
Furthermore, as Eng. Kemper was pointing out, perceived loudness is different from acoustic/electric energy (LOL this sounds like guitar models): if I raise/lower a tone in a range where the ear (whose?) is less sensitive, loudness and energy will vary in a different way.
Last but not least, harmonic spectrum (hence the difference between loudness and energy) depends on the instrument: a neck LP PU will produce energy in a wide different window than position IV on a Strat 
Mhhh... I don't think it might work.
Hey, I figure if engineer Kemper can figure out how to model an amp with such precision, he can certainly come close at normalizing volumes ... 
I hear you. My post was more related to the impossibility to determine a satisfactory algorithm to reach the goal
