I don't understand what you did here, did you activate a -3dB limiter?
The absolute position of the gain knobs, on the amp or on the mixer, don't ensure that you don't clip, it doesn't even lower the maximum power of the amp or the maximum signal out of the mixer, all it does is lower the gain. Think of it like this, if it took 1V (volt) of music at the input of the amp to get the maximum power when the gain is open all the way, then if you dial it back 50% (12 oclock) then it would take 2V at the amps input to get maximum power out of it, that's all the gain knobs do. One more thing, it doesn't matter where in the sound chain the clipping occured, in the mixer, in the amp, for all the speaker cares is whether there is clipping or not. So I need to ask you again, how often do you see the clip lights on the amp blinking? how about on the mixer?
It might be wise to install a compressor especially for unpredictable occasonal shouter, do you have one available?
What speakers do you have? are more getting fried on the pits or in the grandstand? high frequency drivers getting fried or low frequency drivers?
I have never seen a clip lite on the amp. What clipping I have seen has always been at the mixer and only a "light" flashing indication. the horns that blow are over the grandstand which are nearer. I have some horns that are radio shack 8ohm w/30v transformers tapped at 30v. they never blow. the atlas apx40tn's are always the culprits. they are tapped at 40w. the scoring tower is a bustle of activity during a race so I'm not always able to monitor the equip like I need to I guess. I appreciate you assistance immenslely.