Mac: Sig 12 MTK - Some applications will not honor designated system output channels
I recently picked up a Signature 12 MTK. I'm using it with an iMac running Mojave 10.14.1. I have the mixer set to be the system input and output. Using the Audio Midi Setup application I've configured the speakers to use channels 11/12 as specified in the Soundcraft Recording Guide PDF.
Where I'm running into problems is that some apps will NOT honor these settings even though they are defined as the system settings. For example, Chrome, Safari and Spotify playback audio perfectly through the channels 11/12. However, Firefox and Discord (and some other applications) do not. If I enable USB RTN on channels 1/2 I'll hear audio from those applications there instead of 11/12. That's a problem since I'm using those channels for inputs. Ideally all system audio would route to 11/12 as I've specified.
Since the issue not specific to any one application it doesn't seem to be related to any one specific application but rather something at the system level.
Any help or ideas?