It says it right there.
What level of compatibility exists between XP and Windows Vista™ drivers?
Default Driver Model: WDM
As with Windows NT, Windows 2000 and Windows XP, the foundation of Windows Windows Vista™ is the Windows NT kernel, and as with Windows 2000 and Windows XP, the default driver model is the Windows Driver Model (WDM). This portion of Windows Vista™ has remained remarkably unchanged with Windows XP.
WDM Port Class Models
Also, as with Windows 2000 and Windows XP, the foundation of any WDM audio device driver has remained unchanged. All PCI WDM audio drivers are based upon the WDM audio "Port Class" and Windows Windows Vista™™ supports all Windows XP "Mini Port" models, including "Wave Cyclic" and "Wave PCI". Also, all USB / 1394 WDM audio drivers are based upon "Stream Class" or "A/V Stream".
WDM Kernel Streaming
As a result of this, any WDM driver that was built under Windows XP should generally work as is under Windows Windows Vista™ without a recompile. Also, any user mode programs that use "WDM Kernel Streaming" (such as Cakewalk SONAR) in Windows XP would work exactly the same under Windows Windows Vista™™, when run on top of the driver that was built for Windows XP.
Audio kernel, WDM stays the same, so if kernel is there so is the streaming to it. WASAPI is nothing but another layer on the top of it. And speaking of buggy, WASAPI still has a long way to iron out all the wrinkles. Peter, creator of KS and WASAPI foobar2000 plugins, even put the latest WASAPI version in "sandbox" to avoid OS crashes.
Edited by Andrew_WOT - 11/19/12 at 9:39am