Hello,
I am live streaming a concert and need the audio input to be a mix of the soundboard and the mic, does anybody know how to do this?  Im assuming I need some kind of splitter with volume adjustment for each channel.  Please let me know if you have any info!  Thanks.

You will need to record the audio separately and re-combine it in post.
OSMO doesn't have the capability to do what you are after. - A mixer will output line levels, not microphone levels.

^ ^ he is live streaming, he doesn't have the luxury of post.

Get yourself a portable field mixer. They run on a couple of AA batteries and will do what you need. Pricey though for a good one...

https://www.bhphotovideo.com/c/p ... ct_Field_Mixer.html

You would be better off hiring a sound man (plus equipment) to do the job.