Funny you mention Realtek; almost all the audio chipsets I've ever had were all Realtek-- never once did I have any quality or reliability issues with the drivers. In fact, the Realtek drivers I've used (including ethernet) have all been the most reliable of all drivers I've ever installed. And this includes pro audio drivers (like M-Audio, etc).
Regarding MME/DirectSound-- you might be surprised to learn that both MME and DirectSound are emulated by software in Vista and 7. In other words, DS is already deprecated in favour of WASAPI, so moving to DirectSound wouldn't be a big step up. But this is actually kind of irrelevant either way-- because since both are emulated by Windows, not the drivers (at least, they shouldn't be emulated by your drivers), they are going to work until Windows officially says "MME is no longer shipped"-- so there's at least a few more years of life in the architecture. I wouldn't be surprised if some Windows code uses MME, too.
The fact that the Xonar DG has trouble with MME specifically seems like a very isolated case. Your link is also Xonar DG drivers... I've never seen MME specific audio playback issues with drivers from any other chipset. It might be fair to say "Khaled fix the audio stack so that vendor compatibility will be improved"-- but the reality is, it's really just this one card/chipset that's causing an issue. The card itself is faulty (or some driver, or some configuration of the drivers).
