TitaniumEye has all the variables listed except one, and all need to be checked unless you accidentally fix it along the way.

Have you ever successfully introduced a signal into the back of the Onkyo? Since all three don't respond, it could be that. Maybe Onkyo needs the carrier stripped, maybe not. I'd try a Xantech sensor output hooked into the rear of the Onkyo just to test that a standard signal will work. Better would be a Xantech sensor and distribution block, where you supply an LED signal to the jack on the Onkyo. The Xantech doesn't strip the carrier, so if Xantech works, an RP6 output would work.

Also, look up the specs on a Xantech 79410. That's to be used when a straight IR wired signal doesn't work. If they list Onkyo as working with that unit, then indeed a standard IR signal won't work.