>> What about mounting the Piezo tweeter on the top the speaker
>> cabinet in a time aligned version (ala BMW)?The drivers are already physically aligned, if that's what you mean. The versions containing piezo tweeters have no passive crossover and instead only incorporate a small value inductor which is too small to appreciably change phase. In this manner, the system can be considered to be "crossoverless." Further, the physical offsets of the diaphragms are almost zero, so the two sources are at nearly identical distance to the listener on-axis, or off-axis at any angle in the horizontal plane.
There's more about time alignment in the collection of posts below.
>> Where did the name PI come from?
This is a federally registered trademark and was first used in the seventies. I chose the name because of the number of times this value is used in the calculations used to align the box and crossover.