I found this useful webpage which has surprisingly good information on Audyssey:
https://audyssey.zendesk.com/hc/en-us/sections/202387323-Audyssey-101
Regarding the different versions:
MultEQ XT32: Our newest and most accurate room correction solution with more than ten thousand individual control points allowing finer details of the room’s problems to be captured and corrected. The ultra high resolution filters are applied to all channels including the subwoofers, with the most obvious benefit being heard in the low frequency range where correction is needed the most.
MultEQ XT: Our advanced resolution room correction solution with high resolution equalization filters for satellites and subwoofers. Most products with MultEQ XT are installer-ready and can be calibrated by an Audyssey Registered Installer to provide even higher performance for even the most demanding large or odd-shaped rooms.
MultEQ: Our standard resolution room correction solution that uses mid-level resolution filters for satellites and subwoofers.
2EQ: Our basic resolution room correction solution that uses basic resolution filters for the satellites, but does not apply a filter to the subwoofers.
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From what I can see it is very much worthwhile to get the best MultEQ version you can as this has a huge impact on sound quality - I don't think the DACs and Amps in these Denon units are very different. When I was looking for an inexpensive AVR I ended up with the the x1500h precisely due to the MultEQ XT, which was much better than than competing correction systems.
It's worth noting that the AVR Amir reviewed uses
MultEQ XT32 which is the best one Denon offers. Below that they offer 2 units with MultEQ XT, and below that they offer a zillion units with MultEQ.