it is most likely your routing setup in the behringer.. first make sure you have X32 ASIO outputs selected in vMix then make sure you have the USB card returns in the behringer allocated to channels on the desk..

if you use X32 edit go to the routing/inputs screen and where it has the card column across the top you see 1-8, 9-16, 17-24, 25-32.. if you have selected ASIO outputs 1&2 in vmix and you make the selecttion between card column 1-8 with channel row 17-24 this means you should see outputs 1&2 from vMix on channels 17-18 in X32.. using this sort of routing you can leave the first 16 mixer channels as local inputs (X32 pre amps) and channels 17 and up can be used for USB returns from software.. from there you should be able to hear all the signals in headphones or X32 busses/outputs as needed..


there are various other ways of setting this up also which may be more suitable once you are familiar with it.. if you have the newer X32 firmware you dont need to use blocks of 8 channels you can route per channel etc..