I did a similar Double Din installation in my '07 (5. 9) with a Kenwood DDX-7019. The '07 wiring, at least the radio part, is just like the '06.
I purchased all of the parts brand-new on E-Bay for a substantial discount over normal retail.
I got a "Carbon Fiber" (Sport) nav radio bezel from a supplier named "leeautoparts" for about $90. It is really silver with a painted on grid like pattern. It doesn't look much like carbon fiber, but In my opinion, it looks better than the fake wood grain alternative. It is less distracting than the original bright silver one, which creates too much glare.
I also Purchased the double-din to nav radio adapter with a harness kit from a supplier named "integration_solutions" for about $100. I had to talk to the guy there to get the proper harness. There is different harness for the basic factory radio and the fancy one.
The hardest part is soldering up the harness adapter using the harness for the new head unit and the harness adapter. Solder it right, double check, and use heat shrink on all connections. The rest is plug and play. You are making this adapter so you don't have to hack the factory wiring. I didn't have to touch a single factory wire.
With the proper parts, this installation is pretty easy. It only took me about 2-3 hours and I was taking my time. However, I did not replace the speakers.
Getting the dash bezel off is a little tricky. You have to start by taking the console thing around the transfer case/gear shift off first, then work your way up taking the rest of the bottom center dash covers off. Finally, a few parts later, you get to the two hidden screws with the heads facing down that secure the radio bezel. Take them out then pull the bezel. It might be a little tight to come off.
There is a lot of room in there, but I still had to tuck some of my extra goodies under the front seat lower bin. With a few screws, the bin comes out and there is a couple of inches under it. I was able to stash the Kenwood add-on HD / Satellite Radio tuner and blue tooth module, under there. With this Kenwood unit the Garmin nav part is also a separate box. I put it in the lower seat bin so I can access the SD card slot in case new maps need loaded.
There are also some speaker holes up on the dash, which will be empty if you have be cheap radio. They are located under the front bezel right at the windshield. This bezel simply snaps on and off.
That's everything I remember...
Good luck.