Thoughts on the most difficult instruments for speakers to reproduce?

I don't think any one instrument is that difficult compared to complex orchestral pieces.  That's why you will rarely, if ever, hear orchestral music played at shows.   It's always something simple like Bach cello suites, Musica Nuda, some "girl and guitar" stuff.  Well, not always, but most of the time.  

Is there a definitive answer? Or is it all of the above / prior? Thanks.

@nonoise Nice to see your mention of Upright Bass and Oud.

I find most speakers having difficulty presenting the size of the piano on the stage same with vertical instruments like double bass. The sound may be close but the overall experience is not very real as the fingers move up and down the neck. 

Thanks for the excellent comments, interesting they lean mostly to piano. I agree, but IMO systems generally recreate piano sound that, while lacking, is still pleasurable to listen to. In my original post I was thinking more of instruments that are “off” in otherwise excellent recordings, enough to make you hit the switch.

Anyway, this has me thinking that any equipment audition absolutely needs to include bringing along familiar recordings that are difficult to reproduce. This will help greatly to narrow down the selection and spot significant strengths and weaknesses (especially in speakers).

I went to a high-end audio shop recently and auditioned a well-respected tube integrated and well-reviewed speakers (combined about $13K). The owner started by playing the Blood S&T Spinning Wheel opening horns (digital), truly a horrifically hyped disaster. It sounded like a screeching crow being attacked mid-air by a hawk…just unbelievable. That’s what convinced me that dealer supplied material is no way to audition equipment, and not bringing my own was a missed opportunity. There were some challenging recordings I could have brought that would have given the equipment a chance to shine…or not.

(jmcgrogan2, you’re dead on about massed strings and digital. I did some compares and you’re right the difference is striking. Goes to show that dig, though getting very good, is not yet on par with vinyl).
JL