If you don’t need stereo mixes, you can use the left and right outs of the 3 stereo mixes as mono outs by panning channels hard left or right, or center for both outs. It’s a workaround, but cheaper than a stage box.
You can convert one of the groups to a mix and send that to your alt out. Convert another group to a mix and PAFL that permanently through your headphones out. Works for me…
The QU SB does not have an ALT OUT per say but a fixed matrix 1-2 out sending a group switched to mix mode to matrix would get you to 8 outs, the headphone gets you 9.
The stereo panning works, just a little more to keep of what is going where.