Just reading about your problem and I know that I had what sounds to be the same problem, U (fireteam chat) does not work also.
I’m assuming from your post that you edited both the “wm_quickmessage.menu” & “wm_quickmessagealt.menu” files.
When I 1st did our sound pack I followed logic and edited both files, this will work fine if you only adding a few extra menus. The problem starts when you start adding more menus and use up letters in the “wm_quickmessage.menu” file. Don’t bother trying to edit the letters is just a waste of your time.
The fix I used is simple only edit the “wm_quickmessagealt.menu” and use the original “wm_quickmessage.menu” file from the pak0.pk3.
Now that should will fix the T Y & U not working. I assume from your message when you say “all works except if I put our custom sound pak in the etpub directory” that if you move the new mod pack back to your ETPUB folder that anyone new connecting will be able to download it.