AssumedPseudonym and I have run into some odd issues while working on SNAPSS. The current test code successfully overrides audio.....but it overwrites the base sound even when the extension is not selected. There's also been some odd behaviour with things not working sometimes...and while it's probably an illusion, I could swear that the replacement sound gets a little louder over the first couple of seconds of continuous firing...but that's probably just me. Suffice to say though, there's some issues with how the game handles attempts to mess with the stock sounds.
While the proof-of-concept code AP's come up with works pretty well, we obviously can't make anything worthy of release until the audio system issues are ironed out.
For details, see our SNAPSS thread on the RegDev board, starting at the 7th post. A possibly related issue: http://ministry.kronosaur.com/record.hexm?id=3022
More specifically, the mod replaces the vanilla sounds with silent WAV files and includes copies of the vanilla sounds and the one custom sound. Except for the resource entities, the code itself does not overwrite anything in the game.
This was a problem encountered for the Star Castle remake mod at Xelerus, too.
This was fixed in one of the 1.7 betas.