KnownUn, I’m not an expert with Ableton/Redux, but I’m sure it is possible to route all your audio from other tracks through Redux because Redux has this fellow:
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Why not just add a ‘mastering Redux’ to a midi track (with a line input device and any mastering effects in the chain you like…)
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and then alter the audio output routing of all the other tracks to feed into your ‘mastering Redux’ aux in/sidechain (which flows through the line input and subsequent effects) and output Redux to the Ableton master? Also see this along a similar line -> https://forum.renoise.com/t/can-i-use-redux-as-a-vst-effect/46096 