ATC or Audio Note (2-way)

In ATC's case, the level of engineering expertise applied to drivers, crossover and their integration sort of tells you it's not realistically possible to "better" their design effort without equal test gear, facility and experience.  If you change it, it will be "different" which will most likely NOT be better, just different. 

I think sometimes the people that talk about driver swapping are overlooking the differences in efficiency of the driver itself in the previous driver vs new driver and overall impact of this issue on driver selection.  Small differences of 1/2 dB to 1dB in efficiency in the driver itself applied across the entire segment of the response curve allocated to that driver.  Its effectively like turning the entire midrange up or down, or the entire top end (above crossover point) up or down.  Even if you could possibly match the response of the driver itself (which is remote), the efficiency issue alone could change the entire character of the speaker.  This can have the effect of massive amount of EQ, changing a speaker's entire sound from "bright" to one that's "dark" instantly, or bass heavy to bass light, or mid forward to mid back.

Brad   

ATC's are not midrange centric, they are not "smiley curve" sounding as so many speakers are.  Smiley curves sell MUCH better than flat speakers so they are vastly more popular.  Manufacturers know this as most are not in the business to build the best speaker, but to sell the best selling speaker.  If you like music, bass boosted smiley curve actually reduces resolution by elevating bass unrealistically compared to "heart" of the music: voice, piano, violin, guitar.  The midrange now sounds reduced, pushed in back, not like the band or orchestra or instrument really sounds.   This is why many in the high end "accurate" camp use piano for demo.  Its easy to hear changes to EQ on piano.