I use Ableton Live and I want to use my 104M as a send in all my channels. I usually send audio from a synth through it and then record in my sound card. In other words I don’t know how to use it on the sounds coming from Ableton.
Create a “Return Track” then drag and drop the “external effect” from the effects browser. In the settings for the effect, you will choose the audio input and output channel, as well as tweak the latency. Then to send a specific Insturment to the 104, use that “send amount” “knob” about the level in the mixer, next to the pan.