This took quite a bit of hunting, I hope you appreciate it
That wasn't the first time there was a Musical in Sam & Max game [http://www.youtube.com/watch?v=zE75yAilJw8]. It's at about the 5:15 minute point, and they used Redbook Audio off of the game disc to do it which is why syncing was difficult.
Suffice to say, musical numbers in games are
awesome if you can pull them off.
Lest we forget, the Final Fantasy 3 Opera scene [http://www.youtube.com/watch?v=KuvSDedrtKM]. Leave it to Squaresoft not to let a little thing like inability to carry digitized voice stop them!