Exactly. There are electronics in the receiver so you can't just bypass it with a cable. The easiest way is to just point an emitter from the C4 output at the receiver, heat shrink or tape it if you want to restrict the IR light. Otherwise you have to worry about voltage levels, signal pins, and modulated/baseband as mentioned and you risk damaging one or the other. All IR ports are not created equal despite the fact that most use 3.5mm jacks.