I have a Focusrite Scarlett 4i4 (which includes the 2-channel loopback). If you ever want the option of routing multiple channels to another app, MacOS has some other great options. I’m using the open source BlackHole, which creates a new audio driver in MacOS.
You then create an ‘Aggregate Device’ in the Mac Audio MIDI Setup, containing both the Focusrite (ordered first) then the BlackHole:
Within GP I then use the Aggregate device as my audio input and output. The first 6 ins are the Focusrite, the next 16 are the BlackHole. The first 4 outputs are the Focusrite, the next 16 are the BlackHole.
This will allow you to route multiple separate channels from GP to any other app.
The performance I get (latency) is the same as the Focusrite loopback channels.