The Bard would be an interesting way to go. I'd love to hear all of the songs he could learn to play.
I like the idea of the bard being able to learn different songs--but it's just like the idea of a "sneaky" bard--you have be careful. If you have a character who can learn a multitude of songs that he can use in different settings at will, then the character is functionally a mage, just swapping "songs" for "spells."
I'd keep the music thing as a general skill that can be used more like an item. It's helpful in certain situations, but the bard is a smart guy--he already knows the best song to use for a given scenario. I wouldn't leave it up to player choice.
The ultimate goal would be a class that feels just as distinct from the classic three as they do from each other. I would argue that the Paladin from QFG, while cool, didn't succeed in this regard, as it was basically just a fighter with a few unique plot scenarios and "spells."