Yes, I understand what it means to have dual inputs on the eq. But, you have to have something that tells the changer, "Play disc 4, track 7" Otherwise the changer is nothing but a giant paper weight.
Check out your changer manufacturer's sites and see if they have an external controller for the changer (a long cable and a small remote control at one end) that you can put somewhere near the HU. Then you would need a changer-signal to FM frequency converter to play music from the changer. It plays the changer signal at certain frequency that you can pick with your HU set on tuner and that dedicated changer frequency.