To answer your last question first...yes, it is the Metra trim ring from Circuit City. Metra also makes an identical trim ring that's plastic instead of metal and is a little less expensive. You can find it online. I bought one, and broke it because I didn't know what I was doing. You have to remove the 996's outer case and slide the trim ring on from the back. Had I done so, it would have worked fine. So I said "oh darn" or something like that and got the metal one.
As for interfacing it with the nav system to display on the screen...I'm betting it's possible. I read about guys exploiting the OnStar signal to interface with the 996 and provide a GPS input, and I look at the front page of Icom's IC-7000 brochure where it's mounted in a vehicle (a right-hand drive Mercedes?) and the display is repeated on the vehicle's nav screen, and I think that someone could probably figure out how to do it.
The thing is, I'm already displaying my iPod information on the nav screen and I can see where it might get to the point where there's too much information being overlaid on the nav display. If you're curious, the iPod interface is a Neucleus NC-X2i and can be found at
http://www.logjamelectronics.com. They have them for many vehicles, and it displays the iPod info on the screen (or display of your non-nav radio) and allows you to control song selection with the steering wheel controls. The mount for the iPod is a Brodit ProClip. You choose the holder for whichever device you have. They not only have them for iPods, but just about anything you might want to mount -- phone, PDA, video screen, whatever. Then you choose the mount based on the year, make and model of vehicle, and where exactly on your dash or console you want it mounted. The US distributor is
http://www.proclipusa.com. Not cheap, but it looks nice and all works well. The smaller display behind is a RayTel TellPhone 4000 Bluetooth interface. The current model in that class is the 4200, and they go all the way up to a 5500vi, which uses a iDrive-style wireless pointing device and displays call information on -- you guessed it -- the vehicle's nav screen. You can look into those at
http://www.tellphone.com.
Pretty soon we'll need a Garmin 1000-style instrument panel in our cars to manage all the information. Not that that would bother me!