Files stored in the game have no extensions. WAV files seem to have 4 bytes of appended data, which is easy to get rid of, at extraction time. Files also have no compression applied to them it seems.
weird as this may sound, I'd just like to throw in a random thanks here for you (and everyone else) continuing to work on figuring out old weird formats like this.
Wait, wasn't there going to be a HD remake of MDK?
Tell me true, Wikipedia:
"On June 24, 2010, Interplay announced that it is planning to release MDK2 to the Wii platform through its WiiWare service. An updated version of the game, called MDK2 HD, will be released for PC exclusively on Beamdog."
Oh, it was one of the games Interplay announced. So it presumably doesn't actually exist, at least not in the way games are normally conceived as existing (that is, as part of reality).