the qx model years you are looking at have one theater package. you have headrests in the back and up front you can watch media there when parked. there are ways to get around that restriction, but out from the factory you can only watch media up front when the car is parked with the parking brake on.
the theatre system allows each screen to have on a different source, so you could watch a video from a thumbdrive up front, the left rear screen can watch a dvd, and the right screen can play xbox or a ps4.
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HMBC- Hydraulic Body Motion Control.
https://www.youtube.com/watch?v=nmfE65D6ZXg
more detail:
https://www.youtube.com/watch?v=EXyALLsxgFk
good review:
https://www.youtube.com/watch?v=doeUj4k8MLA
visuals are better than words.. ;-)
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the 2012 is better in that it has some subtle refinements over the first run 2011 model. i just recommend you look at the 12 year first and, even if it means sacrificing a trim package..
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there are not any major parts that MUST be replaced at a certain intervals. again check the maintenance schedule to see what things are required to be replaced at certain intervals.
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if you have access to a garage and are handy with a wrench, you can do most maintenance things yourself. the service manual is freely available on this site and you can look through it to see how the car is designed.
there is a cat named "PetitFrereArmada " who is an active member her and on other nissan/infiniti forums, he has a 2012 just as i do and has done a lot of DIY maintenance on his own. he will no doubt see this post and offer his experience and recommendations too, so sit tight. its the weekend so give time for others to chime in.
you cant go wrong with the qx,. its a solid car and worth the investment. but like any other car, if its been dogged out, it will need more tlc than one that wasn't.