Hey Shaun,
I have produced several concerts that were recorded and sent to DVD with 5.1.
Don’t think necessarily of recording to 5.1 but rather use additional crowd mics in strategic places to capture the atmosphere that you would want to have mixed into the concert to achieve the atmosphere that you are looking for. I would suggest talking with a studio engineer that will be mixing for 5.1. You know they don’t just mix 6 channels. They pan 20-30 channels and ad reverb to the surrounds and balance the whole project. To do it right with additional mics is not much more ewxpensive and can achieve a much nicer finished project than simply taking board feeds and trying to “create” a surround atmosphere. Also, supply your mixer and masterer a quicktime file of the show for reference.
Jeff