Your setup and your problems are all audio, not MIDI. You are not using MIDI. So this is not really the best place to ask. But let me help you get started...
You probably should start by trying to find out whether your problem is the audio interface or OBS. Is your audio interface working with any other software? For example, can you play sounds out of Apple Music app and hear it through the interface? Can you record into Audacity? If yes, then maybe you have a setting wrong in OBS. If no, then maybe the problem is in the interface settings. Then I suggest you contact M Audio tech support or ask for help on an M-Audio users forum or some general audio recording forum. Or ask for help on an OBS forum.