Just got the Dirac Live license, ran first Dirac Live calibration (9 points because is in my bedroom setup) and calibration ran without a single issue, like perfectly smooth. Switching between Audyssey and Dirac while listening to music is literally shocking. No kidding, it's NIGHT and DAY difference. I'm already contemplating putting for sale my Living room X4700H and getting a second X4800H. I have Dirac Live in my office desk with a miniDSP FLEX TRS and Neumann KH150s + Rythmik Audio E22 subwoofer so I knew what to expect but switching on the fly between Audyssey and Dirac that's another history.
Have you checked levels externally? (obvious things I know!) - just to be sure that psycho-acoustics aren't doing nasty things...
Need to be sure that actual levels at MLP are the same with both configurations, and then you should also check the target curves, that they are matched, as the defaults are different.
Not that I disagree with you, my completely subjective reaction to comparing Audyssey vs Dirac when I swapped over was pretty much the same. (and no, I did not do fully calibrated and instrumented measurements.... I listened to music, and movies, then switched over, listened to the same selections and then switched back and did it again.... - not having an AVR that could do both, it was a more lengthy process switching over!)