Mine arrived from the April drop. It's a pretty phenomenal amp, I can say that much out of the gate. I am currently A/B'ing with the ZDT Jr and it's surprisingly difficult to discern a difference between the two, though the ZDTJ provides a greater sense of soundstage and space, and makes the disparate instruments that comprise music sound a touch more 'cohesive' -- but the 789 beats it out technically; articulate or busy passages of music are more cleanly delineated, and it's so. damn. easy to pick apart all the instrumentation and production. Bass response is overall stronger than the ZDTJ as well, the bass is thick and authoritative.
Like others, I couldn't help but expect cold and clinical from the 789, and it is simply not. The bass is excellent, midbass is sublime, bass drums slap in a way they don't quite manage on the ZDTJ, where it's slightly more diffuse and not as resolving. The 789 is simply articulate, accurate, assured. (AAA?)
I fully expected to just sell off the 789 after a bit of listening and now am faced with a really difficult decision about which one to keep! I like both a lot, they are somewhat different but not nearly to the extent I expected. The ZDTJ does seem to provide a touch more naturalistic or live-like rendition of recordings, where the 789 is just the recording -- and that's that. The more I listen to say jazz or acoustic guitar I find myself appreciating the ZDTJ's only-slightly more liquid detail retrieval, as the 789 can make sax or guitar with certain effects sound, not sibilant, but almost chimey? More 'artificial', anyway... though of course it's safe to say that that's a more accurate representation of the recording to begin with. (But I'm not a stickler for accuracy with equipment, to be honest.)