I have an Asus DX too and i didn't even try out the onboard sound. I don't think onboard sound can match the quality from the DX, they say that the onboard sound on the Asus Maximus V Formula comes close to it but not the same. So given the fact that the Mpower has a lesser audio chip than the Asus i never bothered to even try it out.
i had my doubts that it would be comparable. sound is not going to be a deal breaker for me. over all i looks like a really good board. it would be my first msi though. still a little nervous. but i feel pretty confident from what i've read on it...reviews and this thread. its looking like i'm going to have to order it from amazon, seems newegg sold out. any good deals pop up,plz post