If you're wondering why the l4d1 sound isn't working, here is a fix:

open 709801948.vpk with GCFScape

extract the contents to a new folder (make sure the folder's empty)

go to "sound\music\safe"

copy/paste one of the .wav files in the same folder and rename the new file to "themonsterswithout_l4d1.wav" (if the file you copy/pasted starts with "themonsterswithin," rename the copy/pasted file to "themonsterswithin_l4d1.wav")

go to "sound"

delete "sound.cache"

go to the "bin" folder in your l4d2 directory (usually "C:\Program Files\Steam\steamapps\common\Left 4 Dead 2" on Windows.)

drag and drop the folder onto "vpk.exe". you should have a new vpk file in the root folder of the folder you created earlier

move the vpk file to "left4dead2\addons" DO NOT put the file in "left4dead2\addons\workshop" unless you know what you're doing.

Start Left 4 Dead 2

Enable the mod if it's not enabled already. It should be automatically enabled, but I've had times where it doesn't.

interferes with Tank mods for some reason

He didn't update the other one because it wasn't his account. lol

This http://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=709801948&searchtext=to+be+continued

what does this fix do?