Latest version of vopsound is 2.1 ?
So if you just downloaded it, shouldn't you be putting @vopsound_2.1?
Maybe you should also try:
"E:\Program Files\Steam\Steam.exe" -applaunch 19900 -mod=@Vopblabla
I don't know that ArmA2 app ID, but just send a shortcut to your desktop from steam, or edit the steam shorcut on your games list.
Also, check
this topic and search for topics similar to the ones you are starting in the future. this is also in the wrong section. Have moved to general as this is a general query about installing addons with steam.