First thing I play when testing a system is album entitled 'Cielo e Terra' by Al Di Meola. It is atmospheric mesmerising acoustic guitar music.
Next I play vocal by Dead Can Dance. Then Bitches Brew by Miles Davis, then Inner Mounting Flame by Mahavishnu Orchestra, then the rest if I need to, usually not because by that point things are almost always clear to me. But if you listen to opera and big orchestra, it may make sense to start with that. Just don't expect too much - no system can adequately reproduce the power scale and instrument separation of a full orchestra. They can't record it adequately either, by the way.
Next I play vocal by Dead Can Dance. Then Bitches Brew by Miles Davis, then Inner Mounting Flame by Mahavishnu Orchestra, then the rest if I need to, usually not because by that point things are almost always clear to me. But if you listen to opera and big orchestra, it may make sense to start with that. Just don't expect too much - no system can adequately reproduce the power scale and instrument separation of a full orchestra. They can't record it adequately either, by the way.