You use the multiple outputs on your 1824 and assign the tracks to those outputs in your DAW software. You can do this several ways depending on your DAW’s capabilities. You could just assign the specified tracks to their own output. Vocal track output 3, bass output 4, then plug those outputs to the HP60’s aux input. This is a simple way to give someone’s headphones ‘more me’.
A more complicated method is to create auxiliary mixes using each channel’s aux sends and routing them to a bus in the DAW and then assigning that bus to an output. This is great when you are recording the whole band playing together. Get a decent stereo mix and send that to the HP60 from the main outs (out 1 & 2) then send bus mixes out each additional output (line outs 3-8 go to six input 1-6 on the HP60) now your artists can say, “I need more kick drum” and instead of changing the faders that go to everyone, you adjust their send on the kick channel to add more kick to bus 1 feeding headphone aux 1. If everyone needs to hear more vocals, you can use the fader to adjust the stereo mix that goes to everyone. This is a similar method to stage monitoring, and while it takes longer to setup and mix, your artists will appreciate it more, leading to better performances.