to me this sounds like overloading the analog input(line-in) of the iriver.
your at943s are very sensitive and adding a preamp with additional gain will result in overloading the analog line-in.
you don´t need a preamp for your at943 mics....this is a deadly combination...high sens 2wire mics+preamp+loud rock show.
next time use a bbox only and get the low sens mod(4.7k resistor) from Chris Church or SP.
It´s just too much input your gear is putting into the line-in at these SPL.
you can even get overloaded input when using a preamp while recording speech...yes it happened to me when i was new to preamps etc.
the levelmeters(digital stage) show no risk for clipping BUT the analog stage(line-in) gets overpowered by using too much preamp gain.
yes petur, rockbox´s "safety-clip" is something every recorder should have implemented in its software.
maybe you should change it´s name from "AGC safety-clip" to "safety-clip" or some similar non-misleading expression.
..."AGAO" automatic gain attenuation only...."ASC" automatic safety clip......."AGL"...automatic gain lowering
AGC is known as evil feature for tapers and safety-clip is NO AGC as it lowers levels but never boosts them again.