@Chuck what I have been doing on Reaper to use Redux as an insert is, in this order:
-Adding a Reaeq with no bands that just forwards the audio from output 1/2 to 3/4 (or any higher).
-Using a VST to Mute channel 1/2 (e.g. socalabs channel mute).
-Making Redux input to be channel 3/4, then output to 1/2.
It is suboptimal, but is a better solution and it can be saved as an FX chain.