I'm using BlackHole with Hosting AU. Great for Parametric Equalization and re-routing audio. Built on Audio Unit but easier to use.
I've also seen Source-Nexus, that has plugins for Pro Tools as well as VST/AU, and you can make multiple named drivers. It would work pretty well with Loopback it seems.
After hunting agressively on Google I was stoked when I found Apple's native, in-house solution: AU Lab.
It's actually really clutch.
https://www.apple.com/apple-music/apple-digital-masters/
https://www.apple.com/apple-music/apple-digital-masters/docs...