I was thinking of a plugin that helps with instances bosses where when they "say" something important that has no audio cue, the plugin could monitor for the text in chat and make a "ding" or whatever.
Sounds are not possible in LoTRO from Lua plugins... yet. If all you are looking for is a notification when something appears in chat, check out LoTRO Alerts which allows you to create graphical notifications in response to chat messages.