I find that at shows the test tracks to be used should stress the systems in predetermined ways to find their potential limits.
Thus, songs like The Lofgren guitar track mentioned, Mussorsky's Night at Bare mountain organ music, Chris Jones -No Sanctuary here/Roadhouses and Automobiles, All of You- Xylophone music by the Modern Jazz quartet, Nuages - James Carter, Get your lies straight -Ry Cooder +, Jazz variants by the Ozone percussion Group and great hall recorded vocal like Misa Criolla- Jose Carreras can help to gain a great appreciation of what a given system can do.