The AT822 is a stereo XY which always uses a pair card or hyper card. when you cal something you need to cal from a single point omni mic because they don't have any proximity effect and reproduce freq content accurately in any give space. I don't know if you ever have looked at freq curves for mics. i don't know anyone would consider AT822 flat or almost http://www.microphone-data.com/microphones/at822/!!! it is also not very sensitive and has a very low output.
I think you have a misconception of what a "high end receiver" is. There is just no such thing. when i here high end receiver i think audiophile. ask any one of those audiophile guys if they EQ inserted their playback chain or if a mic came with any of their components. the answer will be no. the proper approach would be treat your room and then make adjustments to your playback system. As far as i know there are not too many hifi EQ's out there. Pioneer makes low end consumer stereo products that appeal to people that one box that does it all. jack of all trades master of none. when you cal a room like that it limits the performance of monitors. your not getting accurate playback. your room would sound 1000 times better it you properly treated it for standing freqs and took the time to understand what your receiver is actually doing and how it cals the system.
You are slightly incorrect. the freq response of the rear speakers doesn't change at all. The rear are usually placed in a high absorption area, low to between the front and rear seats. so you have a perceived sense that your speaker produce not enough high end. you may have some resonate freqs inside the door but really come on, if your concerned about that your music is either too loud which you wouldn't even hear that issue or you have the cheapest POS car in the world! honestly if that is of great concern you should treat your car doors. acoustic conditions will constantly change in a car.
as i said before i am very confident in my ears as i use them every day to make a living. personally i think auto EQ is a waste of time.
This is kind-of correct right up until the last sentence 
The response of auto speakers is grossly influenced by the door (or other surface) they're mounted in. It is basically impossible to properly match a speaker to the "enclosure" in a car (where the "enclosure" is the door or trunk) because you don't control the volume of the cavity (you get handed that) and you usually can't change it with absorption material in the door itself (most of the time you can't use absorption material in the cavity space at all.) What you can (and should) do is try to isolate to the greatest possible extent the rear wave from entering the listening space, and that can usually be accomplished to some degree.
In addition doors are full of things that have resonance frequencies and while you can add dampening to the panels (and should) to dull them you can't do that to everything that has a resonance frequency (which would be pretty-much anything made out of a hard material in there.) This inherently muddies the sound. Car speaker companies don't generally make sealed-back drivers because doing so for low frequencies requires a very large driver and they won't fit. As a result the assumption they are more or less forced to make is that the mounting surface is a flat panel with no resonance, the surface represents an infinite baffle with infinite compliance and no pathway for the back wave to reach the listening position. All three assumptions are false in an actual car door. While the interior of a car is a fairly-absorptive environment the interior of a door itself is NOT.
The problem is exacerbated by the front and rear doors being of different volumes and having different resonances, even if you use the same speakers in both.
Then you add the fact that head units standing alone have one set of EQ controls for both front and rear rather than separate EQ -- unless you put a digital processor between the head unit and amp.
The "auto eq" function, properly implemented, gives you that processor. What it doesn't (unfortunately) give you is the ability to manually adjust things instead of accepting its idea of "right." If you want that you're going to have to buy an outboard unit because I've yet to see a head unit that exposes that to manual user setting (I wish it did!)
As for observations on the mic and receivers he's right. Pioneer makes middle-of-the road and low-end consumer audio gear. You may think differently, but you're wrong.
But -- even a low or middle-of-the-road system, set up properly, will blow a high end system out of the water where the person setting it up and optimizing the room to the extent possible doesn't know what he's doing.
The NEX auto-eq works very well for what it is provided you have a decent full-range omni mic to feed it and a decent set of speakers to produce the sound. It's not perfect but it beats manual adjustment because it can (and does) separately EQ the front and rear channels which cannot be manually done in the head unit.