Hi Harry, welcome to the RME user forum.
What RME interface and what active monitors do you have?
What TotalMix FX version is in use?
Please post a screenshot of TotalMix FX preferences (F2).
I am using these settings; for you it might look a little different, as I am using the latest version, 2.10 alpha 5.
https://www.dropbox.com/scl/fi/frtogdox … h&dl=1

On the active monitor, you can reduce the volume if it has a volume pot.
Some monitors have DIP switches to adjust the input sensitivity to make the signal more silent.
Your RME recording interface might allow you to choose between different reference levels (click the wrench symbol).
Select the reference level with the lowest output volume.
Additionally, lower the output fader and store this routing and setting to a Snapshot.
Save this setup in a workspace file.
You can also use Workspace Quick Select Slots 1-9 (of 30) to store the workspace there additionally.
The benefit is that you can rapidly restore the workspace using a key combination, ALT-1 .. ALT-9 (Apple: use the "option" key).
Another good possibility is to use switchable attenuators, which are neutral to the sound.
Then you can lower the volume, e.g. by -10, -20, -30 dB.
A good, not too expensive product is, for example, this one: https://www.thomann.de/de/jts_ma_123.htm
If you use such an attenuator, it's very likely that the 0 dB setting on the output fader won't hurt anymore,
possible still in combination with lowering the monitor's input sensitivity and choosing a reference level with lower output volume.
See the thread about volume mismatches https://forum.rme-audio.de/viewtopic.php?id=25399
Its also possible to use a monitor controller.
Then you should validate your TM FX preferences; see my screenshot above.
TM FX online help and possibly also the manual will tell you what the purpose of these options is.
EDIT:
- a snapshot saves the routing and port configuration (ref levels, etc)
- a workspace saves all shapshots and the size and location of one or mor instances of TM FX window on the desktop.
These two options I would set in TM FX - Preferences (F2)
Do not load "-----" By this all volume settings are restored as you saved them.
[x] Always init DSP devices with TotalMix FX settings prevents a question, whether you want to load the device settings from the computer or the recording interfaces. This only happens when you changed the settings in standalone mode on the device. Otherwise the last settings are always restores by the last settings file.
The disable double-click fader ensures, that e.g. the output fader with a reduced volume jumps to 0 dB, which can be very loud if you did not fix the volume mismatch with all the proposed measures here in my posting.
With Reduce volume peaks on Snapshot load I did not make any experience so far. I would take this as an option to experiment,
whether this brings you extra safety. If you solved the volume mismatch as proposed, then this option should not be needed.
Please note: its always beneficial to save safe volume settings to all 8 Snapshots.
Should you select another Snapshot with higher volume you might run again into volume issues.
With Workspace Quick Select it is similar but not the same. If you didn't save a Workspace to WQS Slot 1-9, then nothing gets changed/restored (using e.g. ALT-1..9) if there was no such workspace file previously written.
BR Ramses - HDSPe MADI FX, M-1620 Pro D, 12Mic, UFX III, ADI-2 Pro FS R BE, Nuendo 15, Win10 IoT Ent