I have conquered pulseaudio. With this I can record input and output in one stream while both are in use e.g. by discord.
Adding these 6 lines to the end of /etc/pulse/default.pa FINALLY permits me to record mic input and computer output.
The programs I use are pavucontrol and audio-recorder.
Set audio-recorder's source to "User defined audio source" and set that to OutSink and MicSink.
Ensure that the value of source=0 is your stereo monitor index & source=1 is your mic input via "pacmd list-sources"
load-module module-null-sink sink_name=OutSink
update-sink-proplist OutSink device.description=OutSink
load-module module-loopback source=0 sink=OutSink
load-module module-null-sink sink_name=MicSink
update-sink-proplist MicSink device.description=MicSink
load-module module-loopback source=1 sink=MicSink