I'm not familiar with that plugin, but have you considered using mIRC with the Invision wrapper? It's pretty easy to configure and will do what you want with your mp3's. It's also much more dynamic than trillian. Just a suggestion. I'll shut up now.
There are literally hundreds of audio scripts for mIRC. Most of which are EASILY configurable, especially if you know how to change colors in mIRC. (CTRL K)
Try looking for some sort of configuration screen. I use the Winamp plugin for Trillian Pro which allows me to change both the command trigger (/music) and the text that is displayed (/me is listening to %s.mp3)