As fa as I know, if you would like to apply default sound settings to all users, using the registry maybe useful.
Scan the HKEY_USERS registry hive for all users (names look similar to S-1-5-19).
The key HKEY_USERS\S-1-5-19\AppEvents\Schemes\Apps.Default contains all the definitions for the sounds of that user.
For example, you will find the logon sound under WindowsLogon.Current, whose (Default) value is %SystemRoot%\media\Windows Logon Sound.wav.
Change it to any other file that Windows can play (normally .wav).
Hope above information can help you.