I think that I would be re-playing what I listened the day before just cos I would be familiar with the material. But taking the question like the "ideal" best tracks to test the player I would say:
1. "Chan Chan" from the album Buena Vista Social Club specially to check the detail from the Compay Segundo voice in the background.
2. "Sorrow" - Pink Floyd in the version of the live album PULSE, to check the guitar intro, which has a extreme wide sound, and for the overall sound of the album.
3. "Giorgio by Moroder" - Daft Punk from their new album Random Access Memories, cos I love the track specially the second part when it becomes really intense and I'd really love to see how well the player can handle it.