Even worse is trying to find any API references on MSDN its as if Microsoft want the site to be unsearchable (this coming from a gamedev who spends all day using DirectX/Xaudio/DirectSound and wanting to find something especially for some of our older games which still use DirectSound/DirectX9 and I have to fix some obscure bug or performance issue and can never find any info quickly as I more use DX11/XAudio :[).
If you are after the old DirectSound API reference but on the MSDN their is the old archive section and it contains the DirectSound reference
http://msdn.microsoft.com/en-us/library/ee416960(v=vs.85).aspx
Also as a side not for windows vista onwards Microsoft completely changed the audio stack so if you do use DirectSound for games it is not hardware accelerated (if you have audio hardware that is) and is emulated via software :[. However XAudio fixes that and is quite a competent API in its own right :]
As for legacy API references for DirectX7/8 they arent backed up anywhere as far as I can tell and even than theirs not many reasons to wanna go back to them as going back as far as 9 allows you to support back to XP. And for learning its annoying as 10/11 were major overhauls to the API and 12 is looking to be a even bigger (and much needed) change again :]
The 9 documentation is still up aswell.
http://msdn.microsoft.com/en-us/library/windows/desktop/bb219837(v=vs.85).aspx
also first post on gaf finally had my account activated after being a longtime lurker!!!!