Is your headset set as the default audio output for Windows? Not sure how changing an input would affect the output, and only some of it when the music and interface noises still work.
I’ve just run some more tests based on what you’ve just said. (Using the PA44 Seminole and EGMC as my departure airport each time to keep it the same).
Default sound settings = MSFS set to Sound Blaster Z (default)
- Load MSFS, change sound card to onboard (not default) and carry on playing = Sound stays working
- Restart MSFS = Sound NOT working
- While MSFS is still running, change sound card to Sound Blaster Z (default) and carry on playing = Sound stays NOT working
- Restart MSFS = Sound working
Bug report to be filed then…