RME products have no special sound or house sound. Differences between converters are minimal, a bigger influence has possibly the analog stage behind it, which brings the whole thing to line level.
The measured values of all newer RME products are on a very high level, and RME is also one of the few companies that communicates such measured values to the customer. If there are any subtle differences in sound, then this may be a very subjective matter.
If you attach such importance to it, then you should, in my opinion, also test with your ears in your environment, considering best practices, to be able to exclude psychoacoustic phenomena.
You now say (if I understood correctly) that you do not have the requirements and premises of a professional mastering studio, then I think that you would have no disadvantage with any of the mentioned RME products. No matter if UFX II or UFX III.
All the discussions about whether FS-clock makes an audible difference already happened years ago regarding ADI-2 Pro vs ADI-2 Pro FS. The consensus in the forum was that there would be measurable, but not audible differences.
So, it is unclear to me, why you have any fears getting possibly the wrong product for your demands. I would get either UFX III or UFX II in terms of current or future interface / port needs.
If you think that you require the latest converters with best specs and richest options for any kind of fine-tuning,
then I propose the integration of an ADI-2 Pro FS R BE or even ADI 2/4 Pro SE via ADAT or AES into your setup.
These units give you the possibility to select D/A filters according to your taste or demand and on top of that
give you a lot of additional and useful options.
Some examples:
- 4 different reference levels, auto ref level keeps dynamics and SNR high over a wider volume range
- with the "bit test" you can check whether your audio chain works lossless
The ADI-2 * series of reference converters are designed in a way that they remove any jitter from audio arriving at any digital input. Then it refreshes the clock signal and uses its FS clock for the final D/A conversion.
So maybe the solution for you is to integrate an ADI-2 Pro FS R BE or ADI-2/4 Pro SE into your environment, no matter whether this is an UFX II or UFX III.
The following of my blog articles might be of interest to you:
https://www.tonstudio-forum.de/blog/Ent … our-Setup/
https://www.tonstudio-forum.de/blog/Ent … ses-EN-DE/
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14