^ I agree with the advice with nulldogmas. Getting the rest of the concert even-sounding as he said is your priority.
To that end: your "Wowie Zowie" problem may not be "unrelated". If that guy is much louder than the music in your recording, it will prevent you from raising the level of the overall concert, and whatever amount you do raise it will make his outbursts all the more annoying.
The first step I do in any post work is to go through the entire concert and apply limiting to any places of loud audience noises, applause near mics, etc. so that the non-musical things are knocked down to the level of the music (or at least close to that). I usually do this in Audacity using the Hard Limiter with the dB limit set by ear, and with the Residue Level set to 0.7 to soften the limiter. I am very careful to do this such that the music itself is not being affected. I usually need to experiment with the dB limit to get to this point without introducing clipping.http://ttmanual.audacityteam.org/man/Hard_Limiter
Once the non-musical noises are knocked down, my next step is to select the entire recording, then use the Amplify affect to raise the max level to near 0 dBFS. (I could use Normalize for this which is what I'm really doing, but I like to keep track of exactly how much I'm adjusting the level, and the Normalize effect doesn't allow you to see that.)
In your case, the complication is that first 5 seconds which will prevent the second step from happening. If there's no music or anything significant there, I would definitely delete it. If you need to keep it, I would do everything I've said above but do the gain raise for the entire concert selected except for those 5 seconds. Then you could work on those 5 seconds separately, possibly doing a simple gain reduction to match the rest of the concert.