Snell XA eXpanded array

Hi guys.
I find this solution very interesting and it seems to work really well. I would like to know more about it. From the measurements on Stereophile, the speakers using it seems to have really really well behaved off axis response, especially XA 90 PS. I think the designer is on here, speaker dave? I tried mailing him on here but was unable to do so unfortunately.
I am thinking i want to build something similiar myself. Something more akin to the XA90 than the XA reference because of size.

What drivers were used in the XA 90 and the Reference?
What distance between drivers?
Does drivers used in this type array need to hold any specific characteristics?
The crossovers seems to be LR2 electrical and LR4 acoustic. Anything more interesting in the crossovers?

Thanks. Hopefully the creator of these marvelous things chime in, if he is on here 🙂