since it's so new you'll have a hard time finding one that will do what you want.
Anyways if your ripping a movie you can use AC3 which is surround sound. You just copy right from the dvd pretty much. Music cdroms, to the best of my knowledge, are not aviable in 5.1 formats, they are strictly stereo only.
You can also use a superior codec to mp3 such as Ogg Vorbis which always has had the ability to handle up to 255 descrete audio channels. (254.1 surround sound?).