XAudio2 within the Windows SDK (which includes DirectX 10 in Windows 7 onward) is different to XAudio2 in the DirectX 9 SDK.
Functionally they're the same, but they're defined / initialised differently meaning they're not compatible without changing the references...
This is actually fine in Dark BASIC Professional (GameGuru) Source, as you have access to said definitions; but with AppGameKit "Tier 2" all of that is handled within the Platform Static Lib.
Although if you look at Common.h., every OTHER Platform clearly uses OpenAL; which Windows could also be using.
Why they've made extra work for themselves by using XAudio on Windows is baffling to me.
I mean if they're going to rewrite the Audio Backend to be Windows Specific., why not switch to using DirectX 12 instead of Vulkan for the Graphics, Maths, etc.?
Yet even still the fact that they rely on a Deprecated VERSION of the DirectX SDK (which as noted is now part of the Windows SDK, with XAudio Support still; but it's handled differently to load), well that just has me scratching my head more.
The reliance of the DBP Source on the DirectX 9 SDK is one of the key factors that makes it SO difficult to simply Open > Build the Source., as that SDK isn't exactly "Compatible" with Visual Studio 2015 onward or Windows 8 onward.
But at least there it makes sense, as it was built on that and changing it is a MAJOR rewrite of the Code... as you essentially rewriting huge chunks of almost every Library and the Core.
Where-as for AGK... I can't imagine it'd be more than a 30min Fix to switch to either the Windows SDK version of XAudio.h, or OpenAL.