Control sends on faders in Logic Pro X — Apple Support

When you set the mixer to Sends on Faders, send level replaces channel volume on all instrument and audio channel strips with the same send. Sends on Faders can be a great way to quickly create a headphone mix.

I have been using an aggregate IO device on my Mac for years. I keep changing things around, and think I have a nice, workable solution.

I have my Behringer XR18 “first” for 18 outputs. That is followed by the USB outputs on my Behringer Monitor2USB (output 19-20). I can route a “cue” mix to that stereo pair and easily select it by changing the input button from source 1 to source 2. Great idea. I can also “demo” multiple mix buses if I want to.

I use Rogue Amoeba’s “Soundsource” to route application audio. I can direct output to a device, but I don’t have quite the control that I am looking for just yet. It’s probably time to break out Rogue Amoeba’s “Loopback” (think Soundflower or Dante VIA) to see if I can fine tune output targets to separate channels on the XR18 or Monitor2USB or internal speakers…lots of experiments to be had.