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.