 Despite the fact that there would be no extra features by paying $10, Winamp's popularity and warm reception brought Nullsoft $100,000 a month that year from $10 paper checks in the mail from paying users.In March, Brian Litman, managing co-founder with Uzelac of Advanced Multimedia Products, which by then had been merged into PlayMedia Systems, sent a cease-and-desist letter to Nullsoft, claiming unlawful use of AMP.Nullsoft responded that they had replaced AMP with Nitrane, Nullsoft's proprietary decoder, but Playmedia disputed this.