Starting with Windows Vista hardware acceleration via direct sound was removed. So if a game used direct sound you would get stereo software emulation. In order to get full EAX/hardware accelerated sound in those games you would have to use Creative's ALchemy which intercepted direct sound api requests and translated them to openAL.
The few games that have been released in the last 5 years or so that use EAX do it via openAL so ALchemy isn't required for them.