Have you considered bowhunting? Don't take this the wrong way, I'm not trying to be snide. I just think that if shooting a rifle with hearing protection causes you enough discomfort to become unbearable after two shots, that any rifle you choose would prevent you from shooting well due to the inevitable flinch that the pain of shooting creates.

I'd also wonder if it might be a good idea to go see an otolaryngologist about this hyper-sensitivity to sound. There may be a physiological cause to your problem that they can fix, and an ear specialist would be the place to start.

Mike