It was European I think. It had to do with a piano player, and the set up was the same every episode: He'd come out on stage, sit down at the piano and start playing.

As he went on, he'd start hearing things inside the piano, and climb into it, and then find himself in another world, where he had adventures fighting monsters.

The animation and pacing and general tone were all kind of strange as I remember.

Does this sound familiar to anyone ?? Also, the guy wore a tux, and had glasses and a mustache I think.