Yes, I have searched these and other forums for this apparently somewhat common problem.
Yes, I have applied numerous suggested remedies, including updating my audio drivers, various stuff in the Windows audio settings, ensuring the main playback devices are correct, assigning playback via the CPAN to either the mapper or the correct outputs directly and lastly reinstalling the Q400.
Yes, I am updated to the most current version of the Q400 on Windows 10 in FSX:SE.
No, none of that provided any substantial improvement. I don't know why this is an issue now - this never happened until a few days ago. In the process of switching to and setting up a new joystick, somehow this sound problem came up. It does NOT affect FSX as a whole as environmental sounds like rain will remain there and no vanilla aircraft are affected by this disease as well.
Sound will work from loading a flight up to 15 to 60 minutes in. At some point, all sound WILL cut out and nothing will be left. No main and no headphones playback. The DASH-8 will be completely silent and nothing can be done to bring back any sound. There is nothing in particular that triggers it, it happens in random situations at random times. On the shortest of trips I might get lucky and get on the ground before I lose sound, other times it disappears before I've even started up an engine.
This is really a problem. Without sound there's no joy in flying the aircraft at all. I've spent the past four days trying to troubleshoot this and it's extremely frustrating at this point.