48dB is the max gain for the internal pre. Saftey Clip levels that you see changing vs your raising the gain level is the difference to that max. It actually reflects that figure for all levels of AGC in Rockbox. But as we all know, Saftey Clip NEVER raises gain, so no worries there.
I set Rockbox do that the max gain that can be set is+20dB. +24dB is said to be the last analog step in the pre, then digitally stepped up. That also changes the relation of the above numbers. All this helps in low profile situations. It still up to you to ride the fader up.
Safety Clip would not add to the distortion you experienced. That was either mic placement ( doubtful ), or bass levels. The fact that someone else taped a loud PA without battery box sucessfully doesn't mean that the PA you sat in front of didn't have higher bass response than the samples. The last arena show I sat through ( Alice In Chains, Velvet Revolver ) had HORRIBLE PA bass.....
Why not post an mp3 sample of your pull. Maybe that will show further clues as to the cause of your distortion.