I would set it up just as you do home surround. Its a little different but with a tahoe you are kinda driving a small house around. I would personally put the rear speakers in the pillars by the lift gate at head level or possibly above that at a 15 degree angle downwards. The center channel is up to you. I dont competer in SQ competitions but this is my personal preference. The center channels i hve put in i have facing the straight up. That way it kinda reflects off the windshield before it gets to the passengers. Kinda softens the sound a bit for movies. And with the tweets in the a-pillar are you gonna run that a -3db or 3db. I have found that movies tend to sound a little better to me if they are at -3db. Tends to not be so shrill. You might also find that custom kick pannels are a better way to go with the front speakers. They tend to angle the speakers creating a better sound stage for surround sound.
just my 2 cents but like i said i dont compete in SQ. I like SPL but its not so good for movies. Sorry to say but the head phone idea is crap and will sound like crap to your passengers. NIce to have a wireless set or two if you got kids so they can watch a movie without you having to hear it. Plus kids dont tend to be to picky about sound quality