XAudio2.9 for Windows 7, 8, and 8.1

Official runtime DLL of XAudio2.9 that has support for operating systems prior to Windows 10. Place the DLL in the archive in the same folder as the Classic REbirth DLL and it will allow to use the new sound driver.
NOTE: This is not necessary on Windows 10 as it already ships as a system component, unless you are using a version that doesn't come with it, such as LTSB/LTSC.