Start with destinations
A stream mix is what the audience hears. The headphone mix is what you need to perform. A guest return should contain everything the guest needs except their own incoming voice. Give these outputs distinct names before adding sources.
One source, one capture path
A capture device may provide sound directly to OBS and also enter a Wave Link stream mix. Enabling both creates duplicated audio. Remove one route, make a recording and listen for phasing or a delayed second copy. Muting a monitor output is not necessarily the same as muting the broadcast source.
Loopback is not automatically mix-minus
Loopback returns computer sound to an input. Mix-minus describes a destination with one source deliberately omitted. A device can offer loopback and still need software routing to build a guest return. Check the exact channel assignments and avoid guessing from a feature name.
Protect the monitoring path
Headphones make the first test easier because their output is less likely to enter the microphone acoustically. Software can still recapture a headphone device if it is also the desktop source. Check Monitor and Output carefully: the monitor destination must not feed the same input again.
Test the exported matrix
Speak on each microphone separately, play game sound, bring in a guest and switch music on and off. Record the stream output and test every separate track in a player that can select it. A silent default playback track does not necessarily mean the multitrack file is empty.
For the complete connection plan, use the streaming setup builder. You can keep older equipment in your plan.