Comment by coyote7oni

This is one of several things I'm considering for an Apple Music client I'm writing (they are one of the few streaming services that actually allows such a complete level of API integration, via MusicKit). Apple Music as an app is pretty mediocre, but with a 3rd-party app you can add custom EQ profiles, and even detect the type of device when it connects over Bluetooth and apply the EQ profile automatically on the fly when it is connected, to add it to the DSP processing path.