Two Quick Questions

Does anyone remember what the digital 35mm film replacement devices were called, and has anyone seen any cheap? I have an urge to play with one in my AE-1.

Does anyone know how in-car-entertainment amplifiers are hooked up? They *appear* to rely on the volume control being performed by the ‘head unit’. Which is okay, I guess, but slightly frustrating because I was hoping not to rely on 1970s audio amplification…