On an old MBP I have a similar setup with these two tools:

- https://ju-x.com/hostingau.html

- https://existential.audio/blackhole/

Default output for applications is set to BlackHole's virtual sound device which the "Ext-In / Track D" channel can pick up in Hosting AU as an input. An "AUDynamicsProcessor" and "AUGraphicEQ" stage later (both built-in macOS units) it is sent back to the real output device.