It seems the main value is how MultEQ XT applies both time- and frequency-domain corrections to low frequencies. This makes some sense as room modes and geometry can lead to pretty bumpy bass response.
What does MultEQ XT do at mid- (say ~300Hz) and high-frequencies (above 2K)? Is it mainly frequency response shaping to the target curve? You can't do much time-domain correction at high frequencies, but 300Hz is low enough to do something. How precise is this adjustment, are there typical performance expectations like +/-1 dB within 1/10th octave bands? Obviously the smoothness of the underlying speaker has something to do with this.
2-way speakers often have an abrupt directivity change at crossover, which results in changes to the direct/reflected balance. Waveguides and multi-ways can help, but typically there is still some change at crossover. Can MultEQ XT do anything to address this? Presumably weighting the number of samples on-axis vs. off-axis could "tune" how hot the center seat is relative to the side seats.
I personally do not think it is very audible, but does MultEQ XT try to improve time alignment between between drivers in a multi-way system?
I've mentioned MultEQ XT above, but what are the differences between the different levels of MultEQ at mid- and upper-frequencies?