Assign CUE/PFL in the control room section to i.e. Phones1. And then use CUE in your submix.
See also TotalMix FX Help funtion, search for CUE.
Or i.e. UFX+ handbook chapter 25.3.1
"Another difference to the input and playback channels is the Cue button instead of Solo. A click
on Cue sends the respective Hardware Output’s audio to the Main Out, or any of the Phones
outputs (option Assign / Cue to in the Control Room section). With this any hardware output can
be controlled and listened to through the monitoring output very conveniently."
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14