I can't see using two woofers together in the midrange area at all, horizontally or vertically with the issues that you brought to light.
I guess the next best solution would be to go up in diameter of the midrange driver to a 10" or 12" in an effort to obtain the 100db efficiency goal.

One of my major concerns in using a 12" midrange driver will be the loss of upper midrange to lower treble clarity and frequency extention. I would assume this would complicate the crossover to a 1" exit compression driver and constant directivity horn combination?

Would you please tell me what would be the possible pro's and con's of using this size of woofer for midrange duties mated to a CD and horn for constant directivity?
For the sake of simplicity, I would be able to bi-amp this 15" midbass to 10" or 12" midrange and 1" CD horn arrangement.

Looking at the midrange possibilities, there are a very limited number of drivers available that will work well in the 10" to 12" diameter, especially ones that are affordable.
I think the used market may be where I need to look for a midrange.

Has anyone used the JBL D123 successfully for midrange duties from, say around 100Hz to 1.5kHz before?

Does this driver fair well in the midrange in comparrison to some of the newer crop of drivers. Especially using midrange drivers that are specifically tailored for the frequency range of 100Hz to 200Hz rolling off at 1.5kHz?

Any midrange driver suggestions, or ideas for a three-way speaker system using the JBL 2226 as the midbass to 40Hz, and the Beyma CP385Nd 1" compression driver up high?

Thanks

Norris