acoustic sensitivity depends a lot on a LOT of factors. basically, and to put it simple, your brain has a large area dedicated to every thing, so an area for seeing, an area for hearing. these areas, are divided in small areas, every little of them dedicated to hearing a singe thing, seeing a single thing. the more you exercise, the better it gets.
when you are tired, very tired, basically, areas change their function, so the area for seeing starts to be used to hear, and so. this makes you much more sensitive to loud noises, or frequencies. this has happened due to evolution, and it is a great thing.
everyone who lives a normal life should experience this effect more or less.
now, about k3003, what upgrade could ever be posible? i would enjoy akg putting interchangeable cables, and a better carry case, something like sennheiser ie8 had. the sound, i understand is the best sound yet in an iem. i am still to understand if it is the best sound ever heared.