I've never actually mixed anything for either theater or DVD, but I do descriptive video (mixing narration into completed sound tracks for the sake of the visually impaired). Basically, my job is to match levels with whatever programme I happen to be working on. This means that I sit all day and watch the Master to make sure I don't blow anything out.
Sadly the average mix level tends to run the gamut. It really depends on the kind of show/movie and the era in which it was made. Recent reality shows are L1-Ed bricks with a constant level of -10. The movie Black Hawk Down was similar, with sustained peaks as high as -3, but an average non-action dialogue level of about -20, action dialogue was give or take -10. A River Runs Through It sat at somewhere around -25 to -28, the very occasional peak at -6, and even rarer sustained peak at about -10. The reason for the difference is the date that the L1/L2 were invented, and simply that DAWs can deliver a much greater dynamic range than tape.
As a general rule though, it looks as if most films end up at -20 to -22. Most TV sits around -12 to -16.
The station I work for likes the final product to come out with a dialogue level of -20-ish, and a sustained peak of -10, one shots to -5 or so are OK, but only on the odd occasion. This means that i often have to alter the dynamics of the original. Personally, this breaks my heart. I hate mussing up other people's hard work. But it's what THEY want, so that's what I do.
If I understand you correctly you're printing to DVD but it's going to be played in a theatre, yes? If so, your dynamic range can be much greater because the system and the room (for the most part) has been designed to accommodate it. I may be completely wrong in this, but as long as you're not in the red or reaching for the volume knob in the quiet bits, you should be fine.