I told you what the issue is. The input chip cs8412 can handle only cd quality. No high resolution.
A dac is much more than just a dac-chip. And while the old BB multibit chips are highly regarded they are outdated in the world of high-res streaming. And while the power supply is probably very good, the in and output filters and connections are getting museum worthy. As is the knowledge of the time with which they were made.
I have done lots of modifications on my cd-player and a bunch of DACs. I still have a bunch of old cd-players but they are pretty much useless. Unless as a boat anchor… One of them is a Philips with a famous DAC chip in it, the tda1541. And I have (sold) a lot of Tda1543 DAC with modifications on the output that actually can handle 24-96. I recently brought one for buying and auditioning speakers. Incomparable with the old Philips cd-player. That is like watching a old CRT colour TV compared to a modern 4k flatscreen.
I have done a lot of forum discussions on R2R DACs and a lot of comparisons with people coming over or meetings at others homes. And I do remember how ‘good’ high end cd-players sound. And they nearly would have killed my audio hobby if I didn’t have a great vinyl setup. Which has always sounded better and more engaging. I’ve upgraded my turntable as well and it’s still my reference but digital has upgraded so much over the last years with discrete R2R DACs that it comes ever closer.
I am now using the Rose RS250 internal dac because I am trying out new monoblocks on Magnepans. My regular system has signals going via USB to the Denafrips Ares II dac, to a Gato amp 150 to my own design 1,5 way bipole (2 Ti 3" fullrange + AMT supertweeter) design plus Genesis VI for subwoofers. Yes, I love those Genesis giants from the 90-ies but they have an overcomplicated crossover.
I am now saving to replace the Denafrips Ares II. It’s very good but it was all I could afford a few years ago. It sounds very open and deep. Wide but not like some. Details are all present but not accentuated, a bit like chocolate sirup. If I play DSD on it, it sounds amazing. Only it lacks i²s input and I can’t or won’t modify it.
I was saving for a Venus 12th but now there is a new brand with a new R2R dac called Laiv Harmony. That ticks a lot of boxes and if I read and saw the reviews, is even better.
If the RS250 sounds flat in your setup there is something wrong. The Eversolo D8 has a very similar internal dac. And I do hear soundstage and depth. It might be some setting or cables or whatever. It is a very good dac on itself. However, I prefer the natural sound of an R2R dac, and the signal from the RS250 is good enough for much higher priced DACs.