Zzzzz, here we go.
I kinda don't want to do this, there are a lot of audio reviewers on youtube that to serious DAC reviews with comparisons. Wavetheory, Soundnews, Goldensound, Currawong etc. Just don't check Zeos' May review (i guess we all know that one).
Comparing DAC's is hard for me since i have to switch the DAC in windows and reopen the music player...
I don't want to claim i have more knowledge than these guys. Also i'm at hour 8 out of ~500 for the burn in.
First and foremost: I really don't think that it makes a difference in cheaper headphones (or IEM's, i will keep the RME for that reason), i mostly used the Susvara and that boi is scaling up like nothing else. Even the Utopia seems to not care that much like the Susvara. My 1266 is not a TC, i might upgrade to one, i don't know. It still sounds fantastic on the Spring and Ferrum stack.
I would say: better spatial presentation. Imaging is better. The music is more holographic (i kinda hate that word). It also sounds more "musical". Bass is tighter and more present. I will never do a proper DAC review, also i will 99,9% not buy another DAC, this is my endgame. I will use it in NOS only with 44.1 & 48Khz.
If you ask yourself: Is it worth? Well, do you have a Susvara / 1266 TC / something that is on that tier or higher (you can use a Spring / May for the HE-1 / Aperio etc)...
Have you checked out enough other headphones and you have nothing more to upgrade / sidegrade in terms of headphones? Do you have a really good amp and want to get the last 5-10% difference? Are you all "set in stone" so to speak and want the last piece for the puzzle? Then get an R2R DAC. I've not heard a different one before. Yes, it sounds better than a chip DAC, i also didn't hear a Chord FPGA DAC (it was between that or an R2R for me, in the end i chose the Spring). I don't know how something cheaper like the Gustard R26 sounds, i don't care, the Spring is fantastic and i will keep it probably forever.
I hope that helped a bit, if not, i don't know what to tell you.