DirectSound 3D is deprecated and is not available in Vista and later. DirectSound is just deprecated. I think Microsoft's new method is to use a new API called XAudio.
Creative Audio, whose sound cards used DirectSound 3D, suggests you use OpenAL instead. There's even a wrapper that will wrap DirectSound 3D calls to OpenAL.
I mentioned that.. Xaudio is that Xbox oriented API I was talking about. Most Unreal Engine games use that now rather than OpenAL even though OpenAL is more cross platform and can give better hardware accelerated audio for the most part. The majority of recent UE3 titles use Xaudio in Windows without an option to use anything else. Even if there's entries for it in the .ini files they don't work.
More game still use DirectSound than you might think though even though it's deprecated. I've noticed this because I've wrapped a lot of games in Wine and only Xaudio or OpenAL based ones give true multichannel surround sound when it's enabled in the sound card. On many games that don't including quite a few made within the past five years
I've noticed it's because they use dsound when I would check the error logs and latest Wine revisions it explicitly says it don't have full support for that right now in dsound so it lowers their sound output to two channels.
There's at least one exception though.. Dead Space with an older version of Crossover's Wine engine. Somehow that enables 5.1
dsound channels with that particular game.
By the way that wrapper (ALchemy) you are referring to really only helps people out who have creative labs cards in Windows. It doesn't help out at all in OS X. Perhaps in parallels (or of course bootcamp) when one hooks up an external creative labs card to it. Which speaking of parallels there seems to be a bit more compatibility for software based multichannel dsound there than in Wine at the moment.
Either way multichannel sound support seems to be rather scattered in that most games don't seem to support it properly whether they use Xaudio, Dsound or OpenAL. Creative Labs hasn't really been supporting OpenAL much from what I've read either. It's mostly porting studios that are using it when porting games from Windows to Mac these days from what I can tell.
Many studios just port to basic stereo sound though and others don't test to see if the channels are used correctly. Certain games seem to only have proper multichannel sound by serendipity (such as the Batman Arkham games in OS X).... and many just inherit the problems the game originally had on Windows especially Xaudio based ones being wrapped to OpenAL. Such that even though it's working it doesn't send onscreen dialog for example to the center channel as it should. As with anything there's always exceptions however such as Alan Wake uses Xaudio and has perfect channel usage no matter if ran in Wine or a Parallels VM.
Also, not all OpenAL implementations are made equal and some only support two channels. OpenAL-Soft is the best but not everyone uses it.