I was looking at the Kenwood DNX5120 with Garmin GPS as I have the Avic D3 now. However, I don't like the navi system on the Pioneer AVIC D3 too much. Much too cumbersome to use and search for POI's is terrible. I applied the bypass to be able to input the address while driving. I have a standalone Garmin Nuvi 750 I use when I travel and now that has replaced my AVIC D3 as my primary GPS. I prefer the Garmin interface and ease of use when compared to the generic AVIC. I have someone interested in taking the AVIC off my hands and looking to switch to the Kenwood DNX5120 as it has the volume knob and is IPOD, Bluetooth, XM radio capable with the right add ons. Price is considerable less as well when shopping around.
If you have some extra bucks to spend the, Kenwood DNX-8120 is the one to get if your looking at the Kenwood, however no volume knob. Here is a video on the DNX-8120
DNX-8120