What is the most challenging music to play on a stereo?

I have found over the years that a great test of a hi fi system is music that combines four things: full bodied vocals ( solo & harmonies), acoustic stringed instruments ( like acoustic guitar, banjo, mandolin, violin, stand up bass etc), amplified instruments like guitar, bass guitar , keyboards) & drums.  Not many systems can do this well at realistic volumes in a decent sized room especially when these sound components are all playing together. These very varied sounds & dynamic shadings often tend to get pushed together & loose their inner detail & nuance. 
 

A perfect example of this are the first two Jackson Browne albums which both sound very good on Qobuz if a good album copy is not available. 

Metallica’s Hardwired... to Self-Destruct album is like a tester for any system ability, you can check almost everything including very important index of dynamic range, however this Album-tester is not for tube based amps, very few of them could handle that kind of dynamic. 

The Chariots of Fire theme by Vangelis is one I play for others. Love it !

Happy listening 

Definitely vocals - trying to make Tiny Tim's voice sound better is definitely a step in the right direction

Your system and the music you play on it can be the very best money can buy and still fall very short if your room acoustics suck. Over the many years that I spent chasing the best sound the one and only real lesson I learned was to get your listening room properly tuned to your ears and the system playing the music you enjoy. Every room is different and a simple change of your listening position or speaker placement can make a huge difference. Softening the room so you eliminate reflective noise is probably the most beneficial change you could make. Most of us are not able to dedicate that much space and design engineering to our rooms yet we spend massive amounts of money on our systems. You can put a Hemi engine in a VW but that does not make it any better. Get your room right.