Stavs, I have done exactly this comparison. I still own my Uniti1 with updated DAC board. I started looking for its replacement almost a year ago, spent time with an Atom and even a Star, in direct comparison.
I have to say, if one is happy with the Uniti, which I was and still am, I did not hear much difference in it myself. Certainly newer tech is always the dogs danglies, and things get tricky when doing comparisons like this.
The newer platforms of course bring easier ways to update, are shiny and new, maybe a bit more power, and offer moving into the future such things as Quobuz, etc. things that the techie types might fall all over themselves for.
For me, the new Uniti series actually lost a couple things that are important to me, the FM tuner module, and maybe a bit more analog connectivity which I do use often. Especially if comparing more or less the direct replacement Star for my Uniti1. So there was that. I also was not all over the moon with the wonderful volume knob, as I wouldn’t have used it, I do all from my iPad anyway. Also, the fancy display meant nothing to me either. I guess glitz and glamour do not go a long way with me! It all depends if those things are important to you!
Again, sound quality wise, to my ears, it was a wash, subtle at best. In the end, as I went about my comparisons, as well as thinking cost to upgrade, I decided to throw the Nait XS3 and ND5XS2 into the mix. This is where I believe things took on a better sonic improvement, and a definite step up, and I decided to do this as my Uniti1 upgrade. The funny thing is, I actually spent less money doing that than had I went for the Star! So that was a win for me. Yes, it is two boxes instead of one, but the upside is the Nait will last a lifetime, as I have no desire to go more up the ladder, been there, done that. But also, even though the ND5 will be around a good while, this gives me the option to just replace it, not the whole box as I would with Atom, Star etc. seems simpler to me.
Really, the older Uniti’s are really very good, and just because they have been replaced, does not take away from how good they do sound. Providing yours still works and fits the need? Mine has gone back to serving duty in my bedroom, while I listen to the Nait/ND5 almost every day.
I have gone on here really to say this, they all are really good pieces of gear, just depends if you have that so called upgrade itch or not, but if sound quality is the deciding factor only, I don’t think there is all that in it, IMO. I am sure there will be the cries of cloth ears etc. that is okay. Use your own ears, newer is not always better, maybe just different. Have fun and enjoy the path as you go forward! Sorry for my long blathering.