My favorite test CDs are as follows:
Santana, Supernatural: has great percussion,midbass and range, not to mention great sound quality.
Jacques Loussier Trio, Plays Bach: Incredible CD, great fusion of jazz and classical, great recording quality, incredible drum solos.
Al DiMeola,Paco DeLucia,and John Mclaughlan,
Friday night in San Francisco:
An older recording, but incredible flamenco guitar and great imaging/separation.
Eagles, Hell Freezes Over: Again, great sound quality, nice acoustical guitar.