As mentioned at the end of this thread, I'm looking to code a way to capture OnDeviceStateChanged events. I've read through the msdn info, as well as an example they have, but it's frankly over my head. Tracexx's code utilizes some of this stuff, but not this particular method.
The purpose is for triggering code when an audio endpoint is added/removed/changed from the system. GUIRegisterMsg($WM_DEVICECHANGE, 'WM_DEVICECHANGE') can be used for some of these when they are USB related, but not when a bluetooth speaker (for example) connects or disconnects.