I was wondering why directsound was not implemented using openal. As direct3d is implemented on top of opengl. I see three major advantages : openAL is cross-platform, whereas alsa is linux-specific. openAL is (sometimes) hardware-accelerated. Wine would bring directsound hardware acceleration to windows vista :) See http://connect.creativelabs.com/openal/OpenAL%20Wiki/OpenAL%C2%AE%20and%20Wi... for manufacturers which bring hardware accelerated openal drivers...
Plus, wine would benefit of the system's openal configuration. No need to chosse between OSS and ALSA, the user would have done it through his openAL configuration.