You may have noticed that Xtreme uses "Sound Schemes" stored in Public Documents >> Winstep >> Themes [Windows 7]. One easy way to create a new sound scheme (that will retain the old name) is to overwrite the wav files in the sounds folder [make a copy of the original sounds].

What about a sound scheme for HAL9000?

Old dogs like me had the duty to screen the now classic "2001 A Space Odyssey" at least once, which was great because the ending doesn't make a slick of sense (except for Philosophy teachers that saw all kinds of meanings in it). What about using the voice of the onboard computer HAL9000 for a sound scheme? Betcha ya it would be cool to get a "I'm sorry Dave, I'm afraid I can't do that," when trying to save an update to a read-only file.

The question is, could Winstep release the sound clips or would it violate DRM?

You could always just grab the sound clips you want yourself - a quick Google for "Hal 9000 sounds" should dig up a bunch of .wav clips.