What you need to find on a receiver what used to be called the "tape monitor" switch and in and out connections for a tape deck. This configuration was used to allow a high end studio quality tape recorders with three heads the ability to monitor what was recorded downstream from the record head.
You could also put in a graphic equalizer or compander is line instead of the tape recorder. I have not seen this feature in years. Fisher in the old days would have it on all its amps and receivers.
You could place the equalizer between the source (CD player, MP 3 player etc) and the receiver using RCA cables. But, you would have to swap out cables for each device. Radio Shack used to make a switch box with three stereo inputs and one stereo output. You could use this. I am sure other manufacturers make one like it, too.