The biggest problem with Movies and your idea, is that the vocals are all compressed, AND vocal sounds are only a small percentage of total range of sounds heard.
The rest of the soundtracks are totally useless for any sort of comparison to real world music. If I want a system that can reproduce an oboe, or a saxophone.. what good is knowing it can reproduce loud car exhaust, bombs going off, gunshots, various wierd noises? And who knows WHAT that particular actors voice sounds like in real life? Most of us know what musical insturments sound like in real life.
On the other side, for voices, one of my favorite Cds for sound check of a system is PJ Harvey 4 Track Demos.. Her voice.. is 'spectacular' (to say the least)
Then, on the opposite side of the spectrum is Emma Kirby
singing Mozarts' Extante Jubilante.
The main climatic group singing in Rossini's Barber of seville.. the texture, the harmonies... heavenly... awesome.
Nearly anything sung by Maria Callas...
Janis Joplin....
Nina Simone..
Johnny Mathis Early.. Johnny Mathis (yeah he's corny as hell but a good voice)
Mark Murphy, not much singing, but cool, cat cool.
Pavarotti. early p only...
Vocal CAN mean a lot in auditioning a system.. but I would have to skip movie scores, or movies in general.