Here's a quick video showing you how to use Sonar for Streamers OBS.
If you want a detailed version, see below!
This is how to set up Sonar with OBS,
In Sonar enabled Sonar for Streamers!
Next, you would need to pick your Personal Mix and Mic Input. This can be your headset for Persaonal as well as an external Mic or any way you wish to set it up!
You're almost there! The last step to set up Sonar with OBS would be picking in the Stream mix the "SteelSeries - Sonar - Stream"
Hop into OBS Settings, click on Audio, and disable everything. Then, in ‘Mix/Auxillary’, set it to ‘Steelseries Sonar – Stream’.
NOTE: This mix will transfer over from Sonar to OBS, (this will include any levels and configurations you made in your streaming mode) along with your mic sound settings as well.