Thoughts on the most difficult instruments for speakers to reproduce?

Many instrument's sounds are difficult to accurately reproduce but the one that clearly is the most difficult is the piano because of the range, attack of notes and nuances that seems to transcend most other instruments.  I love organ music but I can hardly say that it doesn't sound realistic (except some close to subsonic notes).  If you listen to recorded piano music, it doesn't take a golden ear to tell it's not quite right.

I read this whole thread, and thinking about it, it seems like it's much easier to list instruments that are reproduced successfully by good quality speakers than those that aren't.
I would say sax, trumpet and brass in general are not that hard to get right. Same goes for acoustic guitar, as well as some small percussion instruments like blocks, shakers and bells.
Pianos, violins and other bowed instruments can be dogs to reproduce convincingly. Of course , part of the blame for that goes to the way they are recorded.

Easily , massed symphonic strings .