I'm exploring XAudio2 (the successor of DirectSound) at the moment. When I'm proficient with this, I could contribute some sound system code, if needed.
@Mnenomic: I like C# more than C++, but if you keep portability in mind, C++ should do the job ... maybe you should split wme into a core engine and several standalone modules/"plugins". If you push the DirectSound stuff into an extra module, it could be swapped with an specialized XAudio2 module for Windows 7 / XBox, with a CoreAudio module for MacOs / iPhone or suitable audio modules for linux. Do the same for the video engine and cross platform wme is coming closer ;-)
About Java:
Thinking about Edna, Java seems quite suitable for adventure game engines, BUT the Edna engine ist not even close to WMEs performance.