tough sounds to reproduce ???

cymbals. probably the hardest to get right (particularly if you're using digital; analog has greater luck)

May not be what you are looking for, but one of my recordings has footage from a swamp, and it appears to quantify the noise floor in a system. On another recording, there is a person in a row boat which really highlights the ability to sound stage.

The sound of a woman saying " Honey, why dont you go out and blow $10,000 on some new components, I think youre stuff is getting old..."

I have to diagree with Abstract7. An Ocean I have heard reproduced 'faithfully' at times in my system. But Clapping and thunder I agree is really hard to reproduce to its full relization. People in crowd or a a party could be done. Certain pessages (can't explain) of strings or piano at times sounds incorrect(not just my system). We will ignore the real life dynamics v/s its reproduction topic for this discussion. Good thread!

Yes, I agree that the sound of the piano is very difficult to reproduce correctly. I have heard very few systems that get all the notes (seemingly) right. The overtones and harmonics of the mid and treble notes can really grate or ring or be shrill. I have a couple of piano pieces I always use when auditioning new equipment for just this reason--they usually sound pretty bad unless the equipment is first-rate.