Many games let you specify the audio output, and then adjusts the mixing accordingly. This would be something similar I guess, but the mixing is probably best done at the streaming provider, to save bandwidth and other resources. (For static content like music it only really has to be done once per output type.)

I'd like something like this, I have a vastly different sound setup at home than on the go, but listen to mostly the same tracks. Most sound pretty good on my home setup, but on the go I often find myself adjusting volume up and down between tracks, despite things like normalization being on.