look at the top of each fader, you can set up MIDI channels there.
for the Octa, I use NanoKontrol v2 + USB/MIDI Host… although I’ve been tempted to go for the Faderfox more than once. I love that you can configure everything from the hardware, and that you can have several templates for different setups.
I recently got a Launchcontrol XL for cheap, although I’m using it for an iPad setup, more drone/noise oriented…
the good thing is, I can have 8 user templates, lots of knobs at hand, LED colors configurable for the knobs (only 4 colors, but still super helpful for live use)
the only bad thing is, if you use it standalone (ie. Octatrack) you don’t get any LED feedback on the buttons (usually reserved for AUDIO/MIDI track mutes) they just stay unlit.
that’s kind of a no-go for me… too confusing - NanoKontrol does have button led toggling, although of course if you change a mute from the octa, it won`t refresh… but still, seems like the best option for the money…