What were your thoughts on the Zaph ZA14W09, SB Acoustics SB15NRXC30 and Infinity MRS drivers?
The Zaph would be a contender, but power handling is marginal, even with two, to set against big drivers in a huge speaker. Just enough bandwidth, but would need a notch filter.
The SB unit does not have the required bandwidth.
The infinity is a spare part. Being a planar magnetic integration problems a formidable. I just don't like mating planar magnetic drivers with cone drivers.
For instance I never like the ML hybrids.
This unit is a possible contender, but you would have to use two.
The SEAS excel units are way less then ideal, and really require an active design to use them as midrange. You also have that monstrous 4 kHz break up peak to deal with.
They have good power handling in the low range so with an active design you can get adequate band width. However you still can't get the crossover out of the speech discrimination band.
There really remains a very poor selection of midrange drivers available to the home constructor. The Dynaudio D76 is not available and the ATC mid, the best midrange driver ever made is no longer on the OEM market.