Usually the button functions are defined in the keybind.txt file inside the data.zip of igo, so on many devices you can reallocate the hardware buttons functionality of igo, however I think on the avic the Pioneer shell takes over this control because I tried to modify the default settings in the file and it unfortunately didn't make any operational change.
There is a utility called AEKMapScan which can be run in test mode to display all the relevant hex codes sent by the hardware. I may be wrong in my findings but maybe it gives an idea to anyone who wants to investigate further..