Mac: Send audio to BOTH Blackmagic card and Macbook?

Hi! 

I tend to stream my NLE output to a client via a Blackmagic Monitor 3G and then a Magewell UltraEncode box to be able to have clients collaborate with me via Pixelview or Klash. However, I need to be able to monitor the Blackmagic sound and a Zoom call at the same time. I've tried combining both the Mac audio with the Zoom call and the Blackmagic output via an analog 4 track mixer, but I cannot get rid of the electric noise that happens when I connect it all into a loop. This also happens when all devices run off the Macbook, so it cant be a ground loop issue.

Anyways, ideally I would like to send my Premiere audio to both Blackmagic AND the Adobe Desktop Audio, so that I can monitor it all via the Macbook Line Out. Is it possible to set Output Mapping to something like that?

Or maybe you have a much simpler solution to this? I've also considered using an iPad for the Zoom and connecting that to the 4 track mixer in order to avoid all this, but I would prefer to keep all Software running on the Macbook.