FFT Input does not work when i use headphones

[oddity]

This feels like a weird situation.

I'm using Resolume on windows.
In Preferences -> Audio
I have both "Audio Output Device" and "Audio Input Device" set to "Primary Sound Driver".

Outside of resolume when I set my audio output to play through my desktop speakers (ie when I select the speakers as the sound output in windows), then in resolume FFT input works perfectly.

But if, outside of resolume, I change my audio output to my bluetooth headphones, then within resolume there is no FFT signal.

I have tried all combinations of different devices for "Audio Output Device" and "Audio Input Device" within resolume but nothing makes a difference.
I do have "Left & Right" selected for the "External Audio FFT Input" option.

It would make sense to me that I should be able to just leave the output and input device to "Primary sound driver"... I dont understand why Resolume can read the audio when windows sends it to one output but not to another.

Any thoughts on how to fix this?

[mowgli]

It sounds like your sound input is your microphone, if you use headphones that won't work for obvious reasons.
You'll need an app to route audio internally