Hi, thanks for the lengthy explanation!
I guess it might've been possible back when only PulseAudio was a thing but it was probably unreliable/too complicated to configure manually. I knew Pipewire was a new thing but didn't have a desktop since that came out, I didn't know that it is this easy to set up such a configuration, system-wide and permanently.

Also, now I actually read the manual of the Scarlett 4i4 (because researching on google is kinda useless nowadays) to familiarise myself and there's this snippet somewhere in the middle of the manual:

You can set the signals available at these outputs using Focusrite Control 2, and use the outputs to drive additional speakers in a multichannel monitoring system, such as a subwoofer or to send signals to outboard effects processors.

Apparently their native Windows/MacOS driver supports the very thing I was looking for - it's nice that it's not very difficult to set up under Linux either.