Hello,
I see this gsound parameter as well on our server config (but it's empty), however I don't find this value used anywhere in the connection code, only reading levels and names as far as I see.
To play sound, maybe just don't rely on shrubbot like you try, but call it directly yourself.
Just add something like that near the welcome message print on the connect.lua part:
et.trap_SendConsoleCommand(et.EXEC_APPEND, "playsound \"sound/world/player.wav\";")
You can also play it only for a given player by specifying slot, e.g for player connecting on slot 5:
et.trap_SendConsoleCommand(et.EXEC_APPEND, "playsound 5 \"sound/world/player.wav\";")
Care about relative links. Also check server logs for any error reading the file (check path, permissions).