On an 8000NEX, how does playing a movie (from SD card or USB, or DVD I guess too) work out with GPS running in the background?  Or does it at all?  Will the GPS jump in if you're coming up on a turn?  Obviously this is with the parking brake bypass.  Also, what about the "rear seat video"?  Assume you can have any other functions going on the head unit (GPS, radio, iphone, etc.) and have video pumped there?  Thanks!

You will get verbal only for navi if watching video.

Yes you can have the DVD, SD Card play to the REAR. Except for HDMI

I usually have my USB1 function, NAV and REAR function on most of the time in the car due to the kids.

You will get verbal only for navi if watching video.

How easy is it to switch back to nav if you get an alert?

A button push.

How easy is it to switch back to nav if you get an alert?

Theres a button that says "MAP" on the bottom

I can't speak for rear video, but if I'm watching a video on the head unit and the GPS is about to give an instruction, it will automatically switch from the video to the GPS display for a couple of seconds, and then after the turn is made it will switch back to the video.  It works perfectly!