An interesting thread in regards to this:
https://www.forum.rme-audio.de/viewtopic.php?id=12958

I would tend to spend the money for an UFX+, as RME told about the following advantages compared to UFX:
- analog curcuits and DSPs have been overhauled
- better SNR and THD vallues
- better headphone outputs with only 2 Ohm impedance and with +19 dBU max output Level

So I would assume that the audio quality for analog i/o, where UFX was already great, will be even better in the UFX+.
So maybe very close to the ADI-8 QS.

And on top you will get the following advantages:
USB3/USB2, Thunderbolt with Windows hot-plugging
MADI - Total: 188 channels (94 IN, 94 OUT): 24 analog, 32 ADAT, 4 AES, 128 MADI
DuRec: Better Direct USB Recording (DuRec): up to 76 channels out of 12 analog and 64 MADI inputs
DuRec: Interne Real Time Clock, timestamps for durec files
DuRec: better reliability for slower or "multi partitioned" USB thumb devices
Better Micro Inputs with +18dBU max, no PAD
Micro Inputs with 75 dB Gain Range, 10dB more compared to UCX/UFX and 15dB more compared to 802.
Wordclock BNC switchable to MADI koaxial
MADI split Modus, 32 channels via optical and 32 via coaxial
The two potis on the left directly control volume of phones 9/10 und 11/12.
Fully stand-alone, additional config options compared to UFX.

Then you can use UFX as preamps or ad/da converter in front of the UFX+ and you have a backup unit
or you can sell it .. but better wait until the campain is over in mid of January.

Potentially the ADI-8 QS will have some additional benefits as its specialized for D/A and A/D.
The question is at the end whether this is relavant for your use cases.

The best would be if you test the different devices (UFX, UFX+ and ADI-8 QS) in your own rooms
and then come to a conlcusion for yourself based on our own ears.

Maybe the differences are so minimal, that you even do not recognize it using your headphones or speakers.
Then its simply the question what you regard as more useful for yourself.

The UFX+ at least gives you lots of options for the future, esp. by MADI, no limitations as with ADAT
in terms of sample frequency and more flexibility in terms of cable lenghth (MADI, multimode: 2km).

Hi crimsonnoise
what's your results using both UFX+ and ADI-8QS?
thanks

Maybe we should expect an update of the QS (10 years old now) ?