I have, indeed heard of the man, and I have met him, as well. (I cannot remember how long ago it was, but it was at the CES a few years back, and I have heard his systems...)
When deciding on a mid-range driver, my number one priority is FLATNESS IN THE PASSBAND. As this is the driver that will be reproducing the band that the human ear is MOST sensitive to, it is critical that the driver be as exacting as possible in that area.
I do have a few points to make; observations, really...
1: Finding a GOOD 5.25 inch driver is going to be difficult, at best. 5.25 inch drivers are most often found in the car, and very few manufacturers offer good ones, simply due to their intended purpose in life. I'd HIGHLY recommend hogging your hole out for a 5.5 inch driver... Your possibilites then become FAR more varied and vast, with many more significantly higher-end options, especially.
2: I also recommend 8 ohm drivers for mids. As the distortion from ANY amplifier increases as the impedance goes lower, so too, does it DECREASE as the impedance goes higher. Distortion in (again) the most sensitive band of human hearing. With amplifier power as cheap as it is today, there is no reason you shouldn't be able to find ANY amplifier to provide you with more than adequate power for
any mid/tweeter combination.
3: Kick panels suck. Period. Put the arrays in the doors, you'll be glad you did.
4: The passives alone will NOT be enough to bring your image to the steering wheel. TD is really necessary, to do it properly. Physics tell you that the line lengths from driver to ear are just TOO disparate to do it properly, and passives will not be easy to manipulate after the installation.
5: Can you actually go three way? The difficulty I see with a two-way, especially a two-way with a 5.25 inch driver, is the matching of the drivers... Physics dictate again how high a driver can go without beaming. With a 5.25 inch driver, I'd never go much over 400Hz for extreme off-axis (such as you'd find in a car) listening. Where are you going to find a tweeter that can go that low without blowing up, and STILL go to 15-18K, clean? (This, by the way, is coming from a guy that HAD been a two-way fan forever, then went three way, and is a convert!) Also, your axis is MUCH steeper on the driver's side than the passenger's.
The house is a COMPLETELY different animal. As you are litening on-axis, driver diameter selection becomes less important. Example, the Adire Audio 6.8 is a 7 inch driver, with an upper clean ON-AXIS frequency response of 3.5kHz. I would NEVER use them that high in the car, EVER. Mine happen to be crossed over at 250Hz. Also, in the house, you are equidistant from the drivers (speaker system). The car? Enh... Not so much.
I'm kinda done for now... You have a PM.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."