Quadraphonic — 2 stereo outputs at system level

Mac Pro 2012
OS 10.13.6 (High Sierra)
Software: UR44 v2.1.3
UR44 firmaware v2.12

I am trying to achieve a quadraphonic output at the system level from my UR44. I have 2 sets of speakers I want to hear not only music from DAW but system level outputs like Spotify.

Here is what i have done:

Mix 1 on front room speakers
Mix 2 on backroom speakers

In the dspMixFx Mixer utility software controlling playback of Spotify, I am unable to hear anything out of 3/4
However, If I click the speaker test from the Audio MIDI setup utility, it makes a sound.
I just cant get any other software to play out all 4 channels through the mixer software
When I click “Mix 2” no sound from Spotify, Internet browser and etc.
Am I missing something on setting this up?

I’d like someone to explain to me how to use this Mix 2 feature. The documentation is scarce.