"Merging" multiple audio sources in Windows into single multi-channel virtual source

Noticed this question got 4K views. So thought I'd add what I finally figured out. I'm using a fork of OBS Studio - OBS Studio ME (https://github.com/pkviet/obs-studio/releases) available for Windows and Mac.

You can add a filter for each audio source, called rematrix, which allows you to map that source onto particular channels of your 8-channel configuration. (It supports upto 16 channels actually).

So for example, the 2 channels on the embedded SDI go to channel 1 & 2. The Scarlett 2i2 goes to Channel 3 & 4. So on and so forth.

For those not doing livestreaming and need to combine the audio for some other purpose, OBS can actually output the audio via NDI (which supports 16 channels of audio). OBS also has a monitoring function for each audio source, which can output that audio onto your chosen output audio device. Not sure if this supports more than 2 channels of audio though.

You can achieve that with this or this

I've used both with great success when streaming to twitch and hosting remote lessons to my students

You will be wanting to use a "virtual audio cable" product which allows you to remap inputs to outputs. You may also need a real-time audio mixer in order to process the incoming signals. Reaper may be suitable for this application.