Okay, I have worked with all of those ribbon drivers and offered kits using a couple of them in the past. The new GR Neo 3's have quite a few performance advantages and sound better overall.
So you might consider using them like we did in the Wedgie, NX-Otica, and NX-Treme models.
For the Wedgie we crossed them to four 3" LGK drivers. The voice coil offset on the 3" drivers was 3/4" In other words 3/4" from the surface. So we designed a waveguide for the tweeter that was 3/4" deep to physically align it with the voice coils of the LGK's. That way the crossover design would keep the drivers in phase in front and in back as this was a full open baffle design.
See some Wedgie builds: http://www.audiocircle.com/index.php?topic=135561.0http://www.audiocircle.com/index.php?topic=151056.msg1616048#msg1616048
Initial testing and development: http://www.audiocircle.com/index.php?topic=126112.0
Putting the Neo tweeter in an open baffle really takes it to another level. And no rear for rear ambiance add on's.
with the NX-Otica and NX-Treme models the offset was 1.5" to the voice coil of the larger M165NQ drivers. So a 1.5" deep waveguide was used.
You could do the same thing with your 4" drivers. Just cross to the center two drivers though and allow the additional drivers to cross to them in the 200Hz to 250Hz region where they handle lower ranges and fill in any baffle step loss. This keeps sensitivity high too. And it is ideal to minimize baffle width.
You could even drop in a Wedgie center section complete and let the larger TB drivers handle from 200Hz to 250Hz on down to the mid 80Hz range or so. You could use them in an open baffle too.
Oh, yeah and the GR Neo 3's can be crossed much lower as well. We cross them in the 1,300Hz range in the large waveguide of the NX-Otica and NX-Treme models. So the response all across the vertical plan is almost as flat as the on axis response.