RoC, I haven't heard the AMR DP-777 but I've heard many a top flight DACs and based on those experiences I can say with great conviction that the difference among DAC performance narrows down extremely once you cross the USD 4-5k bracket.
By now, I have also learned that you can buy a DAC blinded, so long as you know two things:
(1) What is the presentation of the DAC.
(2) Whether that presentation will go with the rest of your system/is to your liking.
Currently I have 3 DACs at different price points, and they all change the signature of my system accordingly. However, none of them turns another's signature upside down. They just do slightly different things. And believe me or not, despite the order of magnitude difference among their prices, I can live with any. So narrow has become the gap that any good DAC, once it qualifies as good, sounds good as long as they are in appropriate chain.
Among the top flight DACs I have heard dCS, Goldmund, MBL, Weiss etc. They all sounded great. There was little to fault with them. Choosing one over the other among them for me would just be a matter of system matching.
Going back to the challenge of choosing a DAC blindly, I'd say, it's much safer compared to choosing an amp or speakers blindly. To choose a DAC blindly think over the two points I listed above and you would be safe.
Oh by the way, the most musical DAC I ever heard was none of those expensive DACs, it was a Sonic Frontier. So, if musicality is your thing, hunt down a Sonic Frontier DAC and enjoy a bliss for not that much money. Another good musical DAC at real world prices is Ayon. If money is no object then Goldmund or dCS.