Couple of things
1. don't ignore the pinned post in this forum regarding posting a OBS Studio streaming/recording log when asking for support
2. You haven't mentioned the connecting technology involved (SDI, HDMI, USB, NDI, etc) .. there are many nuances to each.. so hard to advise with so much missing critical information
3. an iMac i7 doesn't say much (sort of like saying a mustang v6... couple be an econobox, or powerhouse... depends)
My general rule of thumb is to get Audio and Video source working outside of OBS Studio (OBS Studio NOT running at all). Use Operating System (OS) native tools to ensure your basic sources are working at OS level. only then configure in OBS Studio
