I've owned the M33 for about two years. I decided to simplify my system. I got tired of the amp/preamp/phono amp/streamer/CD player and all the attendant wiring. I looked at a lot of the better integrated amps. I settled on the NAD because it had ample power to drive my Acoustat 2+2's and everything it does is in the digital domain so very quiet. I also was interested in Dirac, though frankly I thought that I would never use it. That said, the M33 without Dirac is an excellent powerful and transparent amp with none of the nasty characteristics of earlier Class D. The amp is a great deal even without Dirac.
Dirac, however, is a total game changer. I was always skeptical of equalization or "room correction." For every article I read that said it improved the sound, I read another that said just the opposite. I will put this simply. Dirac is superb. After having used it, I just can not see EVER going back to a non-corrected system. In the process of setting up Dirac, I saw that I had 15-20 db peaks and troughs in frequency response in my room. I realized that before Dirac, I was listening to my room, not the loudspeakers.
I have been in this hobby for 45 years, and the NAD M33 is one of an extremely small number of pieces of equipment that for me have been a total revelation and game changer. I can't recommend this unit enough (and, no, I don't work for NAD!). Just don't overlook Dirac. It requires investing a Saturday to figure it all out, but once you learn it, you'll never go back to a non-corrected system.