There are two authors I can name off the top of my head who, like Simp, deal with the desperate, sadistic side of sex and porn:

The first and most obvious being the Marquis De Sade

The second is Peter Sotos , who coincidentally briefly mentions JM Productions/Rob Black/etc. in one of his later books, the title of which I can't recall. (In his opinion JM doesn't go far enough in delivering the degradation promised on their box covers).