I'm fascinated by all of this; I'm pretty sure your use of spatial averaging and mine are for slightly different purposes.
Russ, yes I'm pretty much thinking in terms of coming up with permanent settings to flatten the anechoic response of the speaker, which I understand is not what you're doing. I have no experience getting meaningful measurements in large rooms. I consider meaningful measurements in small rooms impossible, except maybe for near-field (mic 5mm off the dust cap) at low frequencies, which might be helpful for sub alignment when anechoic data aren't available. I'll have more to say eventually but I've got to think about it and have to run now. --Frank