This is a good resource for info on 5.1 mixes: http://duc.avid.com/showthread.php?t=87830
Among his links is this “Model DP564 Multichannel Audio Decoder Userâ€™s Manual” from Dolby:
Model DP564 Multichannel Audio Decoder Userâ€™s Manual
For film work, test noise at reference level should produce an SPL of 85 dBC for each of the main front channels (Left, Center, Right) and 82 dBC for each Surround channel . The lower Surround level is specific to film-style mixing rooms. For television work, test noise at reference level is typically set to produce an SPL ranging from 79 to 82 dBC for each of the main five channels. The lower reference level for television reflects the lower average listening levels preferred by the consumer (typically 70 to 75 dBC)
Often a stereo sound mix for TV uses limiters and compressors and has less dynamics than a theatre mix. This is because it is mixed at a 79 dBC per channel instead of 85 dBC per channel.
A movie theatre mix is also mixed with 20 db of headroom.
A TV mix converted to a 5.1 movie theatre mix will have less dynamics. The best option is to go back to the stems/sources that was used to make the TV mix and mix it again at 85 dBC per channel.
I recommend having all movie theatre mixes done at a professional film mixer that uses the 85 dBC per channel standard.
If you are converting a stereo TV mix to 5.1 mix for DCP use I recommend using Pro tools and a upmixing plugin. You can match the dialogue normalization level, but not the the dynamics of a proper 85 dbC movie theatre mix.