fwiw,
I've seen myHTPC used in conjunction with mamewah.. on my buddy's cocktail... He uses mamewah, but when he wants his cocktail to playback mp3's or video clips or photoalbum or what have you he launches myHTPC via mamewah.
also SageTV, has a hidden undocumented MAME frontend built in that can be enabled...
Im sure there's GOT to be a plugin for mythTV or freevo to act as a frontend (or call an exisiting linux MAME frontend).
*shrug*
rampy