If you have the option in your country to return an item within 14 days or a month, I would simply try out the ADI-2/4 Pro SE. As the saying goes, "The proof of the pudding is in the eating."
I will summarize the many things I've read and experienced in the following words. The differences in current converters are becoming increasingly smaller, but there are slight differences in the representation of musical material. Essentially due to a) the converter in combination with the quality of the analog circuitry directly behind it, bringing the signal to line level, and b) in some converters, the additional possibility to choose between different D/A filters.
Regarding a) on YouTube, mastering engineer Marc Einstmann has made an interesting comparison between the ADI-2 Pro FS (older version) and high-end converters. Depending on the music material, he uses different converters and has also discovered certain qualities in the ADI-2 Pro FS. You should simply listen to it and then compare the prices.
https://www.youtube.com/watch?v=doHG32aXBDY&t=1s
As for b), KaiS has already shared his experiences in the forum, mentioning that he particularly liked the Slow filter of the AKM chip of the ADI-2 Pro FS, as it allows for better acoustic localization of percussive sound sources in the spatial representation of the musical material ("the representation of the stage").
https://forum.rme-audio.de/viewtopic.ph … 41#p198641
Furthermore, RME also considers how to properly control converters from different manufacturers. For example, ensuring sufficient headroom, so that even with signals above 0 dBFS (for example, due to a series of signals close to 0 dBFS, known as overs), there is no clipping/distortion. As far as I recall, this is already implemented in AKM chips by the manufacturer, and RME regulates this through firmware so that a few dB of SNR serve as such headroom protection against overs.
Let's simplify and say "this is the starting point for high-quality, transparent audio conversion".
In addition, the devices have various extremely useful features and unique selling points that you won't find with any other manufacturer, providing additional real added value in daily use, particularly in the area of monitoring. Plus, all the features regarding operating power-hungry headphones and options for their linearization.
I gave you already a few suggestions where to search for information, in my blog articles which highlight a few things, and of course, the very detailed manual. Regarding the topics above, see here:
https://www.youtube.com/watch?v=15Zyuo-cOIk
https://www.youtube.com/watch?v=_Nq9ZGAYTwU
When you consider and review how tirelessly RME has made model improvements in the past 7 years, implementing many customer suggestions and new features for improvement. You simply have to say that the optimal balance between price, quality, and features has been achieved here.
All these changes were only possible by this smart FPGA based design (flashable / re-programmable CPUs) and the willingness of RME to make the good even better.
In summary, the added value of a UFX III is not limited to "possibly minor" sound improvements compared to the purchase price. However, we also know that achieving the last percentage of improvement is always the most expensive. But here, it's still affordable! The devices of the ADI-2 DAC/Pro, 2/4 Pro SE series provide so many advantages for monitoring and other things that I no longer want to do without the ADI-2 Pro FS R BE.
You get something unique for your money at a reasonable and fair price.
In my humble opinion, you should simply give it a try. And if you want another preamp (Neve, etc.), then you seem so ambitious that you'll probably treat yourself to it. It doesn't have to be all purchased at once. Especially, you always need some time to familiarize yourself with new things. Too many new devices could be counterproductive.
Tip: The "SE" in the model name of the ADI-2/4 Pro SE stands for Special Edition. The devices are produced in limited batches depending on demand. So, seize the opportunity when available or be prepared for a longer wait, and currently, prices are not dropping.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14