2002 expedition ipod interface

The PXDP , if used , will eliminate the cd changer. That is all the info i have for you. That piece is made by Periphal.

Anything that would allow me to keep the cd changer...

As far as I know there is no one making an interface that will retain the changer.   It should not be hard to do it, if you have access to a local "reputable" shop that does repairs.   All that they need to do is remove a couple inches of the insulation off of the changer cable.  Either at the changer or at the back of the deck.  There will be up to a dozen wires in the cable.  They will have to probe each wire untill they find the 2 wires with audio on them.  The changer needs to be playing while looking for these wires,  When you find the 2 wires they need to be cut and extended a bit.  Then you will need a Double Pole Double Throw switch or a relay.  Wire the switch so that it will interrupt the changer signal and feed Ipod signal in one position and the other position it will allow the changer signal to go through.