I run a broadcast with a few different parallel components, all running through our vMix installation. We have a (really janky) talkback channel made out of shortcuts that mass-move vMix Calls and our mic inputs to a bus and then solo that bus back to Headphones, but this is suboptimal and really only allows for a single producer to be on a single bus because that bus (or Headphones, or whatever) is mapped to a physical output and can't be changed without restarting vMix. In addition to me, I have a PA who needs to be able to separately hop onto those buses without playing switchboard operator with a headphone cable.

Our setup would become significantly more reliable with a way to express "switch Audio Device channels 3+4 to Bus X" and we'd be happy to go from 4K to Pro for this feature.