DCA groups can not be assigned to mix outputs. A DCA has no audio path it is just a control for any channels or mix master faders.
For you control room speakers you could use the headphone output jack, use a TRS breakout cable that gives you two 1/4 in TS “mono” plugs to feed the amp or directly to the control room speakers if they are self powered.
The headphone level control knob would be your control room volume.
In the IO set up you could assign the PAFL directly to output jacks and you can assign the PAFL level to be the far Right hand master fader.
Doing that you would need to assign another fader to be the master LR fader, all the mix faders are fully assignable.
Using the PAFL would be handy for control room monitors as any time you would PFL a channel it would be in the monitors, without any PAFL selections you would have the main mix output, that can all be set up in the PAFL set up menu.
If you don’t want to bother with having PAFL available in the control room monitors
just use a matrix mix, assign the LR main to the matrix with all other mix sources off, set the LR to PRE, assign the matrix to a pair of outputs and use the matrix master
to control the control room speakers.
