Are you aware that you‘ve completely overdriven the sine waves?

This is 100% obvious as the distortions reach almost full scale.
You would have noticed that the sine waves sound completely distorted if you had listened to them for a second.

Even if this wasn‘t the case, you cannot use just any DAC as signal generator to judge an AD-converter.
The DA‘s own noise and distortions spoil the result.

The other way round, to analyze a DA you need a analog notch filter to reduce the fundamental, else you have your result spoiled by the AD‘s performance.

Yes, here’s what a sine wave spectrum looks like, running through UCX II’s both DA- AND AD-converters, loopback.
Distortions products 100 dB below fundamental:

I did an extensive test of AKM vs ESS.

10 runs of sighted A/Bs (each several minutes with multiple switchings) to learn possible sound characteristics.
Then 100 test runs of blind A/Bs, taking several hours total of testing for which sounds better.

The result: 49:51, no detectable difference.

Sidenote 1:
I found the DA-reconstruction filters, partly same named in both brands, do in fact sound different.
At AKM vs ESS only the filters named “Sharp” do sound the same.
This might lead to audible differences in certain configurations, but this can even happen for AKM vs AKM, ESS vs ESS, etc., if different DA-filters are engaged.

Sidenote 2:
We had Cirrus Logic and AKM when we developed some converters for Stamer.
The specific CL converters did sound good, but I doubt there is a “house sound” of any brand.
A simple ESS vs AKM vs CL vs TI etc. statement leads to nowhere.

Outdated sound, really?

Lol, right, a bot. Compared two UCX II units to a shabby uac-232 and clearly heard more mud and noise in the highs even though UCX II DA was more linear and sounded really good in lows/mids. Maybe that's not just the chip's fault and maybe just UCX II being a bloated circuit design (possibly due to costs & size constraints esp with the amount of IO + some DSP) reveals these weird characteristics but let me tell you I was using my hears so. I don't do audio engineering, but I was simply looking to get a better interface to integrate a sub and do proper alignment with REW. And yeah, I think it made me kinda perplexed when hearing such lack in sound from a device with such markup. Just kinda goofy and also a waste of my time esp with all the marketing out there... And also do mind when I say UCX II, I say UCX II. I can't speak on the DACs, UFX III and babyface... But to me a semi-flagship sounding this weak is not a good look.

In terms of me calling out say ESS or Cirrus is cuz I wouldn't be surprised if for example current ESS implementations in RME are much better 1.. 2. Cirrus because plenty of stupid cheap consumer electronics with those chips still sound okay. It might not be the chips themselves but clearly however is working on them might have certain association that makes them do on average a lil better or who knows it might even come down to basics of economies of scale. I think besides being linear there is the other factor imo of sounding clean and close to mass market hardware that sounds good.

tldr; If the song on a linear device sounds muddier or noisier than a freaking airpods pro2 you can't make any excuses about the engineering marvel of the unit's DA, it's just a fail. And I'm being precise with terms in this instance. I'm specifically referring to the characteristics of the performance of the audio and not the 'tone'. And yes ofc making a da for a standard interconnect is always harder than something like an integrated DA with the driver, but my point still stands.

It’s noticeable that you are the only one consistently reporting such severe issues with the UCX II. Moreover, your posts frequently cross the line in terms of tone, with repeated harsh criticism aimed at both the manufacturer and the product, and this occurs across multiple threads.

As a long-time customer who has successfully used RME products in both studio and high-end HiFi environments for many years, I find it difficult to understand your complaints. You appear to be the only customer experiencing these issues.

Typically, when someone is dissatisfied with a product, they return or exchange it. Providing feedback in such cases is of course perfectly fine, and constructive criticism is always welcome. However, what you’re doing here goes beyond the bounds of reasonable discussion.

"quidiee" is the same person as "oiuoiuoiuoiuo".
I have moved his post about the "outdated sound" and all the replies from the old thread about ESS/AKM differences to this one.