The tuner through function is built into EDX-3. This function helps improve receiver gain, depending on the antenna element length used, and operating frequency. Please read the instruction manuals of Alinco HF transceivers for details. EDX-3 maybe refered to as EDX-2, but connection and operation instructions remain unchanged.
I just adapted my Alinco EDX-2 Tuner to the Icom 7200. I looked at the schematic for both tuners and they seemed to be designed very similar and the interface function is identical. To test my theory I cut off the end of the Alinco cable and temporarily hooked up the wires to the auto tuner interface on the Icom. I then mashed the tuner button, took cover and waited to see what happened next. It worked perfectly! Then I put a new four pin Molex plug on the cable to match the Icom. From the pointed end of the Molex plug the wires are inserted GREEN WHITE RED BLACK. I did not want to give up my Alinco Tuner in favor of the Icom AH-4 because the Alinco is built a bit heavier duty and can handle more power but the PRIMARY reason I did not want to switch tuners is because I did not want to trade 160 meters for 6 meters. The Icom tunes 80 through 6 and the Alinco tunes 160 - 10. I also built a simple trigger interface that will allow me to use any HF radio with the Alinco tuner but it requires a few more steps to tune vs mashing the 'easy button' on the front of the rig.