The August release of the DirectX SDK has been released, and has a beta release of XAudio2. It also includes the DirectX 10.1 Tech Preview. There is also a new release schedule, now Microsoft will release a new version of the SDK 4 times a year. The next 4 releases will be November 2007, March 2008, June 2008, and August 2008. You can read more from the release notes here. Or, download the whole SDK from this page.