Use an AUX out, make sure all the sends on the AUX are at unity. Set it to postfader, so it's mix will change with the mains. The make sure all the sends on the AUX are at unity. The AFL button is for After Fader Listen, and it is what you would use to monitor the AUX output. You are most likely gonna want to use two of the AUX's if you can, one for your L Channel and one for your R channel. If there are groups on this board you could also go that route by routing everything through one of the group pairs and then not routing that to the mains (some boards let you do this, some dont) so that it only send through the group outputs. Nothing came up on google for LXII, so I couldnt get a look at the board to see what it has availoable for output. Is it maybe an LX7 II instead?