I've done this several times. The best way to go is to use a stereo 1/8"->RCA cable. If you run it from the 2-track stereo out on the sound board to the line in on your minisc unit, you'll get the best results. Depending on how loud he's running the sound out of the board into the PA, the volume may be a bit low, but the quality will still be superb. If this isn't possible, use an 1/8" - 1/8" stereo chord and run it out of the headphones output; just make sure the volume is up high enough. But, if it's any kind of a decent board, it should have the 2-track output.