As for your question about the seven π cabinet, I've sent plans so you can take a look for yourself. What you'll gain is 9dB DI and no response anomalies or bottom end rolloff that requires EQ to make it right. Just run it flat, and you can use a nice tube amp if you want. You'll also get a uniform reverberent field, because the directivity of each of the horns is matched at 90°. The sound produced has a very lifelike 3D quality, and it isn't confined to one "sweet spot" but is uniform over a large area of the room. I guess you could say the sweet spot is very large.

This is important for reasons other than a wide listening zone. Sound that is reflected back at you from the walls and objects in the room has the same tonal balance as direct sound does, and it is much more natural than a speaker that doesn't have this quality. When listening to other speakers, if you can walk around the room and the sound changes from location to location, then the room isn't very uniform and sounds reflected back are unnatural, even when listening in the "sweet spot."

Some people try to treat the room to make it as dead as possible, but this is fighting a losing battle. You can fix room problems with room treatments, but you can't fix speaker problems with room treatments. Better to fix the speaker instead. With the seven π loudspeaker, what you get is good response on-axis as well as off-axis, and uniform sound throughout the room.