Collectible Card Game Headquarters

I'm working on replacing the sound effects in 2014. I've successfully replaced most (if not all) sound effects that play in match, but I can't seem to get the UI sound effects (like the main menu confirm and such) to work. The main sound effect files are labeled "START" and "BACK" but when replaced, the default sound effect still plays. I've searched through all of the other misc. folders to see if the devs packed those particular sound effects elsewhere in case those two effects are dummies, but I haven't found anything. I've also ran various other tests, such as keeping the file the exact same size as the original, exact time as the original, replaced it with an empty file, but nothing has worked.

I know misc. modding isn't exactly popular in these parts, but I was hoping someone could help me with this.