I haven't heard the audinist mx1; but I can say that my $220 iBasso D4 with $60 worth of upgraded opamps installed is only a small upgrade over the uDAC-2, while the $399 DACport is another small upgrade above that.
I'm listening right now to my HiFiMan HE-300 headphones with the uDAC-2 and I still think it sounds very good, even after all this time. I do think that the RCA output sound quality is a little above the headphone out sound quality so it's perfect for feeding a bigger amp when you upgrade, and I still think the line out seems to sound very similar to my Pico DAC-only RCA out. I have a hard time telling which DAC is which when feeding my WA6 or Amphora from the line out and comparing them. I still remain impressed with either output of the uDAC-2 for it's low price. It's a definite step up from the original uDAC1 with it's improved imaging and treble extension. I got hold of a modded uDAC-2 with the output resistor removed and it was very slightly improved vs a stock one that Blutarsky has (more transparent with my ES5), and the gold edition I've tried sounds the same as the modded unit, with that very slightly improved transparency and clarity, possibly from the cryo-treatment.
I actually have two of these and my teenage son uses one with his Westone 1, HD600 and HD-25, while I use mine with my Westone ES5, HE-300 and LCD-2. Mine have a very small amount of low volume channel imbalance below 8:45 o'clock, which takes place at volumes lower than I care to listen, and they are both silent with no hiss. It's perfect for my Macbook rig because I feed the RCA out into my Audioengine powered speakers, and when I plug in a headphone it shuts off the RCA output so the speakers go silent.