Then you want to turn off the sound event for messages and go to the Highlight dialog (Alt-B -> Highlight) and set that up for their nicknames instead.
Highlight lines that contain these words:
nick1, nick2, nick3, ... (Don't include the "@")
Match on: Nickname only
Play Sound:
..Choose a sound here..
That won't work for any arbitrary op nickname, you'll have to add each one manually. The other way to do it without knowing the op names is to write a script. Here's an
example of what you'll need (you might have to edit it). Put in Alt-R -> Remotes:
ON *:TEXT:*:#:if ($nick isop #) splay THESOUND.wav
You can /beep instead of /splay. See /help /beep