A few things to consider:
Talk to the band/soundman - find out what is and isnt in the board mix. If its a full mix - you may want to add more ambient room sound, if its a partial vox/bass/kick/ type of mix...you will do better onstage, using your mics to fill in the holes.
Do they use a stage snake? or do they run sound from the stage? If there are a few extra snake channels, you might be able to use them to run the mics on stage.
I've found - the closer I am to the stage - the more even I run the sources...as you move further back, you have to start lowering your room mics just to keep the delay sounding "real" and not ahead of the direct board sound.
Good luck - this is my favorite way to record - especially if you have the luxury to work the same band a lot.