One clue as to what's happening is the ART arrays use the same tweeter as the two π tower. The ART arrays have recessed upper midrange around 2kHz, what I usually call the overtone region. It's the edge of stringed instruments and the rasp of voices. So maybe that's what you're hearing because the two π tower has a little bit higher output in this same area, around 2kHz.The ART Arrays have a bit higher output around 500Hz to 1kHz, but that sounds more like presence. It's upper midrange, the C above middle C and the octave above that. But the second octave above that is where the the ART Arrays tend to fall off and the two π's tend to rise a bit. That is the real difference in tonal balance between these two speakers, not the tweeter but the upper end of the range covered by the midwoofer(s).