This is long, but I hope helpful!
Thanks for the comments and the help. Here is some more info on the video system. First, I was very impressed with HiFi Buys service and installation. They took the entire day and walked through everything with us before they installed. Here are some key things we focused on:
Screens : OH or Headrest? We chose overhead for a couple of reasons. First with the headrest you are limited to about a 5.8" screen. Also you have to buy twice the screens and the installation is about $500 versus $100. While HiFi Buys did not report any problems, I had a couple of dealers say that because the headrests get moved up and down, it can sometimes disrupt the wiring.
Other considerations on the overhead screen. The installer suggested a slight "angle down" mounting because he noticed that my 5y/o would be the primary viewer and this would help with screen viewing angle. HE WAS RIGHT! He was also right about the fact that visually, we would not be able to notice the angle.
Size does matter! We chose a 6.8" screen for 2 reasons. First it's the most common size so it has the best price point. Second, and most important, my wife (the owner, driver, and guard of our new MDX!
) was concerned about blocking the review mirror in both the open and closed position. Our findings: On the 6.8" audiovox overhead that we chose, you can not even see it in the rearview mirror when it is closed. Open, it does block the center of your viewing from the rear view mirror, however, I was happy to see that there was a remaining view (from the rear view mirror) below and to both sides of the screen. Bottom line, someone sitting in the middle seat in the 2nd row block the drivers view twice as much as the OH screen.
Viewing angle : Because of the sun roof, the OH unit has to be mounted back pretty far giving concern about viewing from the sides. I was pleased with the outcome. I can see the screen just fine from all three positions of the 2nd row seating. While I have not tried, I would expect it would be small enough to be a problem for viewing from the third row. If I wanted viewing from the 3rd row as well, I would go with at least an 8 inch screen and just try and find the best price.
DVD Unit: - We also bought the audiovox DVD unit. The installer mounted the unit under the drivers seat (we have the NAV unit under the passengers seat). He suggested and we agreed that rear facing was best. The unit fit nicely and seems to be working well. We are having a little problem with the IR sensor but HiFi buys believes they can solve that with one more brief visit. CAUTION. Be sure to mount the DVD player pretty far under the seat. We are actually having ours moved deeper. We had it mounted so that it could be accessed with the drivers seat in the position for me (back further than my wife). When my wife is driving the player is exposed a little and your feet want to rest right on it's face. A deeper mounting (even if you had to side the seat forward slightly to change DVD's) would be better for the unit.
Remote jacks: At the dealers suggestion we had them wire the second AV input plugs for the OH unit (it will accept 3 inputs) into the center console along with a 140 watt power converter. This is too cool! Just below the rear AC controls are three RCA input jacks and a 110 outlet all custom mounted as if they came OEM. Because the rear of the console angles back towards the from of the car, you can hardly see them unless you are looking for them. This allows us to easily connect a VCR, Xbox, Cam Corder, etc. and get power to it and with the push of one button on the OH unit the input is switched. This was a great suggestion by HiFi buys and well worth the extra $100 they charged for the parts and install. As a bonus, you can plug anything into this outlet that you may desire (coffee maker, blender, etc.).
Wireless headphones. Two sets of wireless headphones came with the audiovox screen and they work great (actually better than expected). An RF Modulator (allows the sound to go through the MDX stereo) DID NOT come with the unit. This was something we didn't think to ask about but are having added for about $100 parts and labor.
Installation. I'm no handy man but I would not have wanted to do this installation. Forget the fact that I don't do wiring at all and this system required a ton of it. HiFi buys (with the experience and tools) spent about 6 - 7 hours installing this system which required removing the drivers seat, the center console, etc. They are now (for free) going to remove the drivers seat again and re-mount the DVD unit because we want it a little further under the seat. Yes we paid about $250 more for the parts than the website noted earlier in this thread, and we paid another $150 - $200 for installation, having it installed has been the best decision made so far.
Bottom line with the RF modulator, the system will cost about $1,300 installed. This is the 6.8" OH audiovox screen, an audiovox DVD player, 2 sets of wireless headphones, RF modulator, and the whole custom power and AV job that was done for the second input source. I would do this again in a heart beat!
Bonus - I hadn't noticed at the time of purchase but the OH audiovox unit has two done lights. HiFi buys wired them into the existing system to they work with the existing dome light perfectly, including dimming them selves off when you close the door!
I don't have a digital camera but I will try an borrow one and post pictures!