I've been through the difficulties with sidechaining the Q3 in Reaper so I understand it can be more complicated with FF plugins, but for the life of me, I cannot find a way to make the external SC on the Pro MB work for an incoming signal on channels 3/4 on Reaper. I've unchecked the Enable MIDI button, but makes no difference. Is it possible to do? If not, why not? Baffled.