Volume mismatches can be solved by using attenuators, see this sticky thread from RME.
https://forum.rme-audio.de/viewtopic.php?id=25399
By this you can reduce the maximum volume at 0dBFS.
EDIT: two examples:
- https://www.thomann.de/de/jts_ma_123.htm -10, -20, -30 dB switchable
- https://www.thomann.de/de/shure_a15as.htm -15, -20, -25 dB switchable
Choose according to attenuation demands / range
You can use this in combination with the two basic things that you can / should do:
- to use a reference level with lower output volume on your analog outputs of your recording interface.
- to lower the sensitivity of your active monitors inputs
Regarding volume control:
- you can assign any pair of stereo channel to the TM FX control room as "Main Out"
- you can use the big volume knob of ARC USB (for operating the TM FX control room) to control the volume
ARC USB can be connected to any USB port of your PC and some recording interfaces offer a special USB port for ARC USB, so that you can use it even in stand-alone mode without a computer connected.
Additional channels of your 5.1 setups can be grouped together in a so-called "fader group".
Then they follow the volume settings of "Main Out" / the volume knob on the interface (and/or ARC USB).
The volume of the other channels of your setup / in your fader group can have other volume settings.
The proportion to the volume of Main Out will be kept when you turn the volume knob.
The new room EQ might be helpful to fine tune the setup by using the EQ and delay settings per channel.
If the recording interface has an FX chip inside, then you get even 3 more bands on top.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14