I'm confused? The fact that you actually posted this question when there are countless threads on every audio website pertaining to this very subject tells me you are the one who seems to be confused. Any member of this forum could probably have guesses what 80% of the responses would be to your question as its always the usual suspects.
My point that you seem to be missing is using demo tracks to audition gear will not tell you a damn thing in regards to how much you will actually enjoy a piece of gear in your system regardless of how well it portrays a list of songs or as one member suggests audience applause. Building a system based on this criteria is asnine to say the least. But to each their own. Good luck professor.