Is there a way to "reposition" the sound source when using headphones? Whenever I use headphones to listen to music or synthetic noise (e.g. one of those white noise / natural sound apps), it sounds like the source is coming from inside my head instead of somewhere "out there".

Is there an app or something that can filter these sounds in real-time and uses 3D audio to "reposition" the sound source? So that for example it sounds like coming from real speakers even though I'm using headphones to listen to it. 

Preferably an affordable app for the Mac and not some fancy pro software that only sound engineers use.
Have you try the Boom 3D app ? Boom 3D allow you to reorganize your speaker, but I never tested it with headphone... You should try the free trial !

https://www.globaldelight.com/boom/index.php