BUG: stereo audio mixdown stripping channels
If I provide AME with file that contains 4 channels of audio, when it exports it to H.264 with a stereo audio channel, it strips out channels 3 and 4 instead of mixing them down into channels 1 and 2 as expected. The help file for Media Encoder says "If you choose fewer channels than are in the master track of a sequence or project, Adobe Media Encoder downmixes the audio"
Antoine Autokroma commented
You can export individual channels with AfterCodecs ! https://autokroma.com/AfterCodecs/