redseed:
If you try to do this, the best thing that can be accomplished is getting a SBD tape... In my opinion, not the best recording you could get...
BUT, and it's a big BUT the worst you could do is:
get arrested
ruin the concert for hundreds or thousands of people
be liable for repairs to the equiptment (not just the mixing board, but the amps, speakers, anything that may be ruined
please don't attempt this...