There are two things to consider. One are the FX Sends, the other the FX Returns. The FX Sends (FXA and FXB buttons) allow sending indvidual channels to the FX machines, but the FX Returns allow only the selection "AUX1-4" and "Main" as destination. This means that whenever an effect return is sent to the four auxes, it will be heard in all (!) auxes. This mixer does not have the option to return effects per aux, like the "bigger" models have.