Rewiring a boombox headphone output to be an Ipod input?

I'm rewiring an old boombox to be able to play music from an ipod. Since it doesn't have an input anywhere on it, I've decided to rewire the headphone output to act as an input for my ipod. I've already gutted the tape player. The headphone out is attached to a circuit board which then connects to the main board, which sends the music to the speakers. I will change the old headphone input wiring to go to the old tape input(same wires). The only problem I can forsee is the circuit board which connects the headphone jack to the wires. Will it keep trying to send music out, or will it let the Ipod's music pass back into the main board? Connection diagram: Ipod -> Double-male audio cable -> Headphone jack -> Circuit Board -> 6 Black wires -> Main board's tape player input -> Speaker

Can you take pictures of the headphone jack circuit board and post them? If it amplifies the sound or turns the sound off when unplugged, it may be more difficult, but its impossible to know without seeing it or a schematic.