The reddit guide appears to similar to use of Pulseaudio modules I posted on the old Manjaro forum
Voicemeeter equivalent for linux is an improved version of earlier posts
Separate Audio Output for Applications
and Recording sound from two microphones?
I can’t use the output to all devices option because my headphones are seen as 2 different pairs on the system
In the previous examples, module-combine-sink is only shown using ‘simultaneous output’ to send audio to 2 sinks
But more sink names can be added to send audio to more than 2 outputs
In your case you need to find the 2 correct sink names for Pulseaudio outputs to headphones
and use 3 sink names with the command to load the Pulseaudio module
pactl load-module module-combine-sink channels=2 slaves=voipmix,(heaphones1),(headphones2)