Yes, TM FX gives you most flexibility for that.
The TM FX window has three rows
- top      - HW inputs
- middle - SW playback channels (from PC/application)
- bottom - HW outputs

Each HW Output has an individual submix.

In submix mode you select an HW output, like e.g. the phones output.
The routing to that output you can directly see from the fader positions of top and /middle row (HW inputs / SW playbacks).

Even smarter, on the right hand side there is a small button "sub", if you activate it, then you only see HW inputs and SW playbacks, that route audio to the selected HW output.

TM FX gives you the great flexibility to route audio either from
- HW inputs in near real-time or
- SW playbacks with a little more latency because of the additional transport through USB

Audio from one or more SW playback channel(s) could be a backing track.
You can organize your DAW project even in a way, to break audio down in peaces to use different outputs for e.g. vocalists, soloists, bass, drums, etc.
In TM FX audio will not be send directly to the physical output of your recording device, audio will 1st of all show up in the middle row under SW playbacks.
And now the magic happens, now you can set for each HW output (bottom row) the routing/submix individually by simply selecing the HW output and then turning the faders of SW playbacks as you like. The vocalist may want to hear himself louder, the bass man maybe his bass louder, etc.

If you have such a backing track and record some more tracks with the vocalist you can route the backing track to him as he prefers. But the monitoring of his recorded voice he should get without latency, so in this case you select the phones output of the vocalist in the bottom row and turn up the fader of HW inputs. By this you route the Mic signal directly to the phones with near-zero latency (only a little latency of the converters, but without the full RTL (round trip latency) over USB that can be big depending on the ASIO buffersize being used.

In short, TM FX is so much better in terms of creating submixes compared to any other products.

You can aösp save and recall the used settings in 8 Snapshots on the right hand side, to get the proper settings for recording, mixing, mastering.

There are also 30 Workspace Quick select slots where you can save the while workspace and recall it with ALT-0, ALT-1 ...
This gives you 8 x 30 = 240 routings and 10 Workspaces (with 8 Snapshots = 80 routings) you can recall by using the keyboard combination ALT-0 .. ALT-9.

Best is to consult TM FX training videos, the manual or also my blog article with a good basic setup.
The relevant information you find in this sticky:
https://forum.rme-audio.de/viewtopic.php?id=34394

Line out >> headphone amp >> happy bandmate

not familiar with that headphone amp but it looks like it will do the job. wow, 8 independent inputs. maybe I'll eventually have to get one

Interesting.  I didn’t know I would need a A/D converter.  Do the analog outputs of the UFX not produce a signal that can be used directly connected to the direct input of one of the 8 channels on the HA8000? Please excuse my ignorance but if I could connect one of those UFX outputs to a studio monitor and hear a signal, why couldn’t I connect that output directly to a headphone amp and hear it thru headphones? Would it not work at all or is it just not great quality?

Oh.  Is it not possible to connect an audio cable directly from UFX Analog 1 to HA8000 Channel 1 Direct Input, UFX AN2 to HA8000 CH2 DI, AN3 > Ch3, and so one and so forth to get 8 different sub mixes?  Obviously, sending a mono signal for each channel on the UFX but I think a mono mix would suffice for band members.

Of course it is. Ramses maybe thought of some different interface here? But UFX has 8 analog outs + the 2 headphone outs, and you can send different submixes to each one if you want to. Either stereo mixes with 2xTS to TRS cables, or mono mixes with TRS to TRS balanced cables, as you suggested.
So you could even send two master stereo mixes + 8 independent mono mixes (6 if your main outs are already in use) or 4 stereo mixes, or any combination of these..

The advantage of using an adat D/A in between, is that you can have longer cable run to your headphone amp using a single adat cable, (+ short cables from D/A to headphone amp) instead of using multiple long TRS cables. However if your headphone amp is sitting next to your UFX, then there's no need at all.

Then you can do the following placement:

Control room-------------------------------------------||--------------- Recording room

UFX+ ---------------------------- 2xADAT (up to ~15m) --------------- Ferrofish----- p01-TS-(mono)
                                             or MADI (up to 2km)                                     ----- p02-TS-(mono)+---TRS-- Phones1 (indiv. submix)
                                                                                                                   ....                                         .....
                                                                                                                   ---- p15-TS-(mono)
                                                                                                                   -----p16-TS-(mono)+---TRS--Phones8 (indiv. submix)

If the Ferrofish D/A converter is placed at a central place in the middle of the musicians, then both, the
- 2xmono/1xstereo cables between Ferro and HA8000 and
- phones cables from HA8000 to phones/musicians
do not be too long ...

These were the ideas behind it
- more individual submixes
- better placement of components (if needed / wanted)

BTW, if you want to record in double speed, then you will need MADI, otherwise you do not get 16 channels to the Ferro.
UFX+ has only two ADAT channels, thats only 8 channels @88.2/96.

Thanks for all the help guys.  I really appreciate it.  I think we’ll start simply at first and if its working for us, I’ll opt for the Ferrofish to take us to the next level.  Very exciting stuff.