Using only built-in macOS functionality, or possibly a Homebrew package, is there any way I can send audio from one music program (eg. iTunes) to a Bluetooth speaker, whilst simultaneously sending the audio from another music program (eg. Spotify) to the local audio device (ie. headphones or a USB-connected sound card)?
Some audio apps have a "Output Audio Device" setting, but neither iTunes nor Spotify has this.
Both a specific solution for the specific case above, and a general approach to sending n number of audio streams to n number of different audio devices (including Bluetooth) is interesting.