I have been following this thread as I'm about to take delivery of my new 2015i Tahoe LT tomorrow.
I have been driving a Honda Pilot Touring model with nav unlock, and an hdmi to RCA converter plugged into my composite inputs in the back of my main console, which is practically the same setup on the Tahoe. I have a composite cable plugged into the outputs, and that cable goes into my main console which just like in the Tahoe, is big and whose lid acts as an arm rest. That cable plugs into the converter box. The converter box has an HDMI input. I have a short HDMI cable going from the converter box plugging into an apple HDMI / lightning (lightning digital AV adapter). From there I have a lightning extension cable going out to my iPhone. All the cables, converter box, lightning AV adapter (other than the initial composite going out from the rear console) are all tucked away in the main storage console compartment. Only the extension cable can be seen coming out of the center main console. Great thing about this, which is the main reason I'm posting is that the converter box is powered by USB... and hopefully that will solve the green line issues that you are experiencing.
I'm also hoping that this set up will work just as great on my new Tahoe, and that I'll be able to mirror my phone to my main screen once I get the unlock. I'm posting some links below.
1) For the converter box on Amazon:
http://www.amazon.com/gp/product/B00DSSCBZ8/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1
2) Some photo bucket photos from a pilot user who is the one who initially came up with the setup I'm using. You'll notice in the pictures that he's using 45 degree inserts for the RCA composite cable (which I'm using as well) to make a cleaner cable extruding from the back of the console.
http://s1345.photobucket.com/user/13Pilot/library/NavTool/NavTool set up for iPhone 5?sort=3&page=3
I'm wondering about the HMI nav/video unlock... Is it a device that goes behind the head unit? Do I have to pull the head unit, and send my device to the vendor for reprogramming? I'm a little confused how this works. Also, I see no instructions for installation on their website. Is installation difficult to do?
Thank you!