Johnk,
I know you've designed with the SEAS Exotic W8 woofer. Have you tried the SEAS Exotic T35 midrange/tweeter? What did you think of its sound? FWIW, I'll be using it above a Jantzen JA-8008 driver (OEM by SEAS) as a midrange with a PHL 5011 (updated version of the 5010 driver used by Nelson Pass as woofer in his original "Rushmore" loudspeaker) on bottom. Only a moderately high efficiency loudspeaker, but a true 92-93dB that'll move lots of air.