I'm planning to spend some extended time with it this weekend, but my initial impression is that I like it about as much as I do my Audio-gd. The Audio-gd is great, but I have a problem with it and my Focal Elex for some reason, and i've only listened to the 789 with the Elex so far. One of the main reasons I bought the other Massdrop amps as well as the THX AAA 789. I think the THX AAA 789 has much greater transparency than the Cavalli's, is less veiled and more resolving. Also seems to have more punch. At this price point, there isn't anything I think is better that I've heard. It's a beast. I love the Elex paired with all three of the Massdrop amps, but this one is certainly special.
I also received a pair of the closed back Focal Elegia's today (Can't wait to see them!) to try out for a week as part of the loaner program @TTVJAudio is hosting. Should be a better headphone to do a direct comparison with my Mr. Speakers Aeon Flow Closed on the NFB-1 so long as I don't get the distortion like I do on the Elex. Either way, I plan to give both a direct comparison using multiple DACs and headphones, and I'll post the impressions here after the week with the Elegia's is up!