But what kind of music is "it"? Needless to say, "it" can vary so vastly...
Right, but the average levels are similar, for this reason there are 2 different scales for dynamic range, one for pop-styles, and one for very dynamic styles such as classical & jazz. You be the judge which suits your production. The ( AFAIK )86 avg still holds true, you just allow yourself 6dB additional headroom when mixing dynamic music. If you are really curious, just read about the K-system at digido.com - Since my explanations are not as well thought out.
And the amount of compression used on a final mix can also vary greatly depending on the inherent dynamics of the music itself.
And you're still below the threshold in either scenario since it is leaning towards more dynamic to begin with - your peaks will be lower, your valleys will be higher if comped to genre or taste, but still below 0. Still able to set your bounce to disk levels appropriately, deliver a mix whether you prefer comp or not.
And regarding a movie soundtrack
Ah, that wasn't clear how I typed it. That would have been the entire program - voice + SFX + Music...
Not closing my mind to the logic of this procedure, but basically I still don't get it, because I don't understand how there can be a generic "it" when there are so many musically stylistic and mix aesthetics as variables.
I'm not the best at writing this stuff out on the fly. Do ask more, it probably makes more sense - if my explanations and weak links are unbearable - try digido.com
Metering to push against 0dB is a really odd concept during track+mix. Very damaging and unnecessary. The adjusted solution would be to monitor at good average levels and preserve your dynamics.
J