Is there a song that showed you something you never knew your system could do?

We put together systems with a reference list of tracks that can test different capabilities; tonality, sound stage, pace, etc. You know the list. 

Once we settle on gear we think is best, we go ahead with our listening.

But once in a while, we put on a song which makes us go, "Wow! I had no idea my system could do *that.*" !

For me, the song was "Recat" by Ricardo Villalobos & Max Loderbauer (Album, RE: ECM, 2011). It showed me the ability of my system to sound positively quadrophonic, to locate sounds way back and behind the listening chair. It was startling.

Has any song has done that for you?
What did it reveal that you hadn't known despite having gotten used to your system for a while?
(And if you can, which element of the system do you think was responsible for this newly-discovered capability?)

If you don't have a song which revealed a capability, perhaps a song which revealed a lack of ability.
I am finally about there. I received the first of two REL subwoofers and got it hooked up yesterday. Listening to everything improved immensely. I was recently introduced to a group called Deep Forest which is I guess World Fusion. There's a song called Savana Dance that did exactly as you described. It felt as if I were sitting in a circle of sound that was coming from my 2.1 soon to be 2.2 system. The drums were moving around the room as if the musicians were dancing around the campfire. They were definitely in front of me and then moved behind me! For all of our complaints sometimes when you think about the ability of a 2 dimensional object giving us 3D listening it is pretty amazing! What made the biggest difference? Hard to say as I did a complete upgrade over the course of a month. The Parasound Halo made my old speakers better. The new speakers which are B&W 606 let the Parasound show it's abilities much more and the sub freed my speakers up to handle the mids and highs better. #Winning! Seriously though, check out Deep Forest. I'm primarily a Rock and Roll guy but you gotta appreciate their music and it is very well recorded.
"Savana Dance" -- great suggestion. Excited to try it and thanks for the detailed description.

There is a Chesky demonstration disk which has musicians enter from rear, right, then move in a circle around your listening chair and then exit. It's pretty amazing.