Hmm am beginning to wonder if my waveOut* problems weren't caused by the same thing ... Have so far managed to run for much longer than i've managed up until this point ...

Well I've gone ahead and implemented the system whereby any calling thread will set a command and then "unwait" a worker thread to execute the command while "waiting" for the return.  Its an entirely lock stepped piece of threading so I just have the thread switching overhead.  I'd rather I didn't have to do this ...

I have an MFC app that I am trying to port over to XAudio2 rather than waveOut* (waveOut has SERIOUS problems under Vista and Windows 7 that don't exist under XP :() Now I note that XAudio2 requires that you initialise COM with the Multithreaded model.  MFC (OLE specifically it seems), on the other hand, requires that you initialise COM ...