NVDA stops speaking completely when you are playing  a song? What program are you using to play songs? My only suspicion would be that your program is switching your headphones into headset mode, so that's effectively another audio device, and NVDA keeps sending speech to the old audio device, which is ignored since your headphones are in headset mode. Not sure if headset mode is the right term - but I mean that mode that for example skype uses to capture audio from your headphones and send audio with lower latency. This mode is known to be different from the normal mode for bluetooth headphones, that typically provides  higher quality and higher latency audio. So maybe try another program to play music or figure out what's the output device for music?

--Tony