BMS 4540ND in a DDS ENG-1 waveguide 20,000-2,000hz (if you can manage front and rear firing, you'll be golden. Sensitivity will be in the 120+dB range if you go dipole)
PHL 1120 500-2,000hz (open baffle dipole, sensitivity increases by 6dB over a box design since its emitting sound from the front and rear. A conservative 102dB sensitivity on the midrange!)
Ciare 18NdW1 (maybe 2? if you want balls) 100-500hz (open baffle dipole, output will depend on baffle width)
This would be one hell of a dipole. Incredible dynamics, output capability, spaciousness, sound quality, and they will have a slightly warm signature that is characteristic of the PHL.
If you want more specifics, send me a PM