My guess (and it's only a guess) is that they connect the preamp section to the amplifier section of the receiver, similar to what you find on NAD receivers. That way, you could disconnect the preamp section from the receiver's amplifier and connect it to another amplifier. Funny, I had an old Marantz around that time, but don't recall the preamp jumpers. On the back of the receiver, is there a "pre-out" jack and an "amp-in" jack?
