I’ve just bought and installed Cubase 7.5 on a new Windows 8.1 system, and the “DirectX full duplex driver” is missing from the VST Audio System menu. This did not happen on my previous installation of Cubase 7 on Windows 7.
I have an external sound card, for which I used the specific driver. However, I sometimes want to work while allowing sounds from other applications to work, for which I required the DirectX full duplex driver.
“Release driver when application is in background” is not a suitable option, since it doesn’t allow both applications to work in the same time.