Well, I've used UFX and UFX+ alone long enough and the converters from the UCX II aren't any worse either.
This would give you an excellent basis for your setup in terms of quality and features that cannot be topped by the competition.
At this point I would like to emphasize that the UCX II really got a lot from the flagship interfaces (UFX II and UFX+), for example
- high quality preamps with 75dB gain
- DURec for standalone and backup recordings on USB disk/ssd/stick
- Clear color display, also ideal for use in standalone mode
- a complete FX section (like the predecessor)
- very good headphone output
- AES I/O has been added
So you have everything you need and still have certain reserves, so that you don't have to buy something new after a while.
You can buy an ADI-2 DAC or Pro FS at some point later and integrate it into this setup in order to enjoy further sophisticated RME features.
> Edit: it seems like as long as I’m not using power hungry planar headphones, the UCX II should be good enough
> by itself. Or I assume I can add an amp if necessary.
Which phones do you mean ? I am using planar headphones and wrote a review about Audeze LCD-2, LCD-X and LCD-3 (which I own). There was absolutely no issue driving these phones with UFX+, ADI-2 Pro FS, Octamic XTC.
To have planar headphone doesn't mean, that you have headphones with high impendance or inefficient drivers ..
Last but not least .. if you are also doing recordings etc .. then it's more important to get a good recording interface with a digital mixer first, so to say UCX II with TotalMix FX.
The ADI-2 DAC pro is 1st of all an USB DAC without TotalMix FX.
The ADI-2 Pro has some more routing features, but also this is much more static compared to the capabilities of TM FX.
Therfore: good recording interface 1st and if you have the money and interest: ADI-2 DAC/Pro on top.
Further information incl. links to excellent RME training videos on youtube which are on the point and do not waste time you can get from this posting: https://forum.rme-audio.de/viewtopic.php?id=34394
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub13