Unlock all of the other cars in the game. Select the San Francisco Drag Race and use the Dodge Concept Viper to set a new time record. Then, enter SOUNDMAX as a name at the high score screen. The Jaguar XK-R "SoundMAX SPX", Jaguar XK-R "Analog Devices", and the Aston Martin DB7 "SoundMAX SPX" will be unlocked in all modes except for story mode.