It's definitely worth it to rent the sound effects CD from MTI. I extracted the WAV files from the CD and loaded them onto my Fantom G7. I created an SFX track in MIDI Maestro for each song where a sound effect was required. The SFX track triggered the correct sound from the sample set on the Fantom in perfect timing with the music. I did manual triggering of sound in the case of single gunshots. Valjean "fires" a rifle when he lets Javert go in "First Attack", and Gavroche is shot multiple times during "Second Attack". Having the sample pad on the Fantom allowed me to trigger these effects in real time. Additionally, the scream that Eponine utters during "Attack On Rue Plumet" is not easy to do night after night. To save our Eponine's voice, I found a royalty-free scream WAV file, and loaded that into the sample set. Again, manually triggering that at just the right time (as our Eponine turned her head and cupped her hands around her face) was pretty realistic!
Putting the sound effects under MIDI control also gave the people running lights, sound, and the slide show one less thing to have to worry about!