Those are nice headunits, I put the model under that one in my daughters Charger and she loves it. I installed a Panasonic in my XF last week. I just chose it because it had a silver pc on the face that matched the XF console color. It has many of the same features as the Pioneer, just no built in BT, but I can add it later. I use the built in crossover functions on the front spkrs and let the amp that I hide behind the Qtr panel trim do the low freq work. It is connected to a 10" Crossfire sub in a transmission line enclosure. It sounds pretty sweet and people are surprised at how much pressure the little 10 creates in the car if I tweek the settings for boom.

Try using the HP crossover function built in to your Pioneer and see how well it makes the front spkrs sound. You will lose the Bass out of the factory rears but a small dedicated sub in the back sounds much better anyway. You could also just run new wire to the factory rears and send low freq straight from the headunit rear outputs. Lots of options with that headunit ...

Here's mine: