My experience with editing VCE files was, back in 2002, very basic. I had to use Microsoft EDIT (DOS aplication) to change some bytes of these files.
Using this EDIT app (EDIT.COM) that still remains in Windows Xp (system32 folder) I was able to get some "patterns" on ASCII bytes and discover some samples used by engine, skids, crash, and other sound that were used in game.
But I had to use EDIT with "open in binary" switch option to see byte values.
Getting it straight, on windows command prompt you write this:
edit /93 pceng1.vce <- for pc sound editing.
edit /100 adeng1.vce <- for ad sound editing.
Then you will see this: (for pc speaker)
Next I show what I had written in 2002 to explain what I had edit and its consequences:

(broken image link)
Note: above pictures show content files that were written by me. EDT file extension is not used on game.
For Adlib(SoundBlaster) its very similar to edit.
Now I will show what I had analysed in sound file content, taking Adlib file as example:
(this is a mod screenshot to show all content bytes on original and mod files in horizontal split screen)
Has you can see there is a STOPSTARENGIBLOWSKIDSCRABUMPCRAS text on first line, spacing these chars in logic words, it identifies 8 words that is the number of rows below the first text line of the file content.
Assuming this, Stop sound sample code corresponds to the first line, Star(t) the second, The third is for Engi(ne) sound and so on.
I don't know what all chars do in each line, I tried to change on by one, but the most relevant were those that I point at pictures above.
And that is some of what I remember of this. All suggestions are welcome to get this sound sampling code revealed.
Cheers