Hi, just thought I'd post the results of two hours of debugging :(
I have a Xonar D2X with the latest drivers on Win7 64bit. I bought DCS:Black Shark on Steam and the menu loaded but as soon as I tried to load a mission or quickstart I got a crash referencing xaudio2_1.dll with exception code c0000005.
I updated directx, tried older drivers, went through the FAQs here, turned off UAC, reinstalled BS, etc. The only thing that worked was uninstalling the driver or disabling the soundcard, which led me to try disabling all the other devices and now it works!
Right click speaker icon in taskbar -> Playback devices. Right click and disable "S/PDIF Pass-through Device" and "ASUS Xonar D2X Converter". You can right click and show disabled devices if you need to enable them later.
Not sure why this works, maybe the old directx dll doesn't understand the extra devices the Xonar driver installs. Hope this saves someone two hours of pain!