We have 6 of these Audix console modules, type 35205. They are labeled "Echo Return Module". These are the ones with the RED knobs in the picture. You can see that 4 of the 6 modules have a set of missing push buttons. If they ever had transformers they are now gone.
They have the following controls:
PFL and AFL push buttons
OFFSET left and right ( which I think is some kind of stereo pan
a Mono/Stereo pot