Insterting an FX on a channel will only let you put that FX on the channel
it is inserted on.
If you select one of the FX send buttons on the upper right hand side of the mixer
the faders will switch to sends on fader mode for that FX, just like they do when you select a mix for monitors.
Just like turning the aux knob on an analog mixer for the aux that the FX unit is patched into.