I downloaded the sample I think the problem is one of frequency not of volume. My meters were hitting around -8 to 0 db and they are calibrated to with in 0.004db
I think that the problem is the mics were not high enough on your body or there was something in front of the mics.. Because they dont sound that muffled ever unless something is blocking the front of them or they are not aimed at the source. I think for loud shows +10 is pretty good on that preamp. The + 30 setting is strictly for acoustic stuff.
On your recording there is a serious bump at 300 to 600hz and one at 125. If you reduce these and boost from 2k all the way up to 15k you will hear what I am talking about. Normally you dont have to do much eq adjustments with my mics but I really feel the mics must have been not aimed properly or you were very close to a turbo sound PA. Where the boxes blue or purple? In the UK there are lots of Turbo sound systems and you have to be very careful because they have beaming mid range for days on them.
especially if you are right beside them. It also sounds like at some point in time the guy doing sound lost the top end on the PA system and if he did it still would have sounded ok... Because if it was turbo sound he would have had the top end crossed over much higher then most other pa systems I believe they cross over at 3.5k and the 10 inch mid speaker goes from 250 to 3.5k very wide range... I can hear the top end coming back and going away in the mix that has to be the sound system or the mics getting uncovered... One of the two.
Chris