It fell out of favour in part due to the fact that you could inadvertently plug your expensive phono cartridge into the speaker output by mistake and fry the cartridge. With those RCA jacks it would be easy to use the switch for ...
let's start with the speakers. These Sansui SP-2700s were, and remain, a hilarious monument to 1970s over-engineering, sporting various parts nearly everywhere. When I look at them sans grills, I picture dozens of Japanese assembly-line workers, bombed after returning from a three-sake lunch...