There is no easy solution to that. If you mix in 5.1, you need a decent 5.1 system for monitoring. Professional film mixing stages use similar equipment as in real cinemas, and they are calibrated with the same mechanism, that means, they also use a cinema processor at fader setting 7 to create the 85db SPL for the calibration. That's the idea of the Dolby level 7 in cinemas - mixing stages and cinemas adhere to the same reference level.

 In theory, you could do that calibration on your own monitoring setup, but it's hard to keep a level/setup discipline on non-pro audio gear, computer soundcards, etc.

The good thing is that you are working in an absolute digital audio reference system - the same 24bits that your computer delivers to your audio card can be transferred 1:1 to a digital cinema system. That was more complicated in the analog film days where a lot of analog reference levels had to be maintained throughout the monitoring and master transfer chain, not to speak of the complex behavior of analog matrix sound systems.

Mattias suggestion to use the EBU128 filter for an analysis is not bad. Common VU type readings are useless, as they do not weigh perceptual aspects of the sound. Peak levels are irrelevant, unless they indicate clipping.

For a monitoring setup, I think it is best to avoid as many analog stages between your computer and speakers as possible. I think the easiest non-pro setup would be to feed up to 8 LPCM channels from a graphics card HDMI/Black Magic Design HDMI output directly into a Home AV receiver. After proper setup, there should be only the AV receivers master volume control that can mess up your reference level. Mark it, and you should have some piece of mind.

A lot of semi and pro audio cards have AES/EBU outputs, but I rarely see 5.1 or 7.1 receivers with discrete multichannel capable AES/EBU inputs, at least not in the price range I could afford.

For people with less ambition to spend extra money on a monitoring system, I actually suggest getting a range of common DCP trailers from a projectionist, e.g. different programm types like dialog, action, music, etc., extract the audio (which is possible as these trailers are unencrypted), and play it on your monitoring system as a reference to your own material.

If reliable monitoring to spec'd levels would be easy, we wouldn't have this discussion. ;-)

- Carsten