Anyway this is going to be shorter..
--on/off switch
THe on/off and the eject switch is from a broken xbox.. The front panel has 9 wires, so i tappped into the ones on my xbox and put the female 9 pin connecter on the back.. took the other front panel and extended then to my dash.. You dont have to do this you only need 2 wires to turn the xbox on and off.. But I wanted the leds to work and maybe one day put the dvd drive in my dash so thats why i ran 9 wires..
--Sound and Video
I have a Clairon flip-screen that has AV in and 5.1 optical in..

--Remote
From what i know the 3rd party remote will not work or will not work properly for XBMP...
If it works for you more power to you.. On ebay the M$ remotes are going for like $10US..
My IR receiver is plug into the two controller port that i install in my dash but you could just crack it open and extended it.. I just still wonder if you could piggy-back the controler like a mem card.. It seem logical..
---Car off playing XBOX
It work fine for me with me car off.. also I have a trunk party awhile back and played it for about 2 hours, also jammin the music pretty loud..
"It stays on for 2 sec then cut off" sound like the power is cut to your sig lighter.. Make sure that you have power to you sig lighter with the key off and not just ACC or RUN
--Pain in the ass to get every thing playing after shutting off
If you mean that the WHOLE XBMPs setting then that a problem with xbmp..
Yes when i shut mine off then on i have to go back to my music or movies and hit play.. But most of my music is setup in playlists so that i can get them going quickly..
For Movies there is a feature that was add about 3 or 4 releases ago or so.. hehe Called Bookmark.. it only works on video but it allows you the put a bookmark of where you left of.. Just hit the TITLE buttton on the remote or the white button on the controller and it will bring up that menu on the botton and then select "Video Settings" in there will be "Create bookmark" which will allow you to start right where you left off at.. The only shitty think is you have to start that movie you where watchin and then you can go the Cycle Bookmarks..
Infuscomus.. that $30 cheaper than the one i was looking at.. still $170 ouch..
Tell me how well it works when you get it.. I still think a Laptop converter will work.. just cant get my friend to let me rip it apart.. O well my 12v to 110 work fine Plus i can put almost any thing into it..
Btw I look at the specs and it pretty strait forward.. only bad part its not going to fit in your xbox.. and i not sure if the xbox connecter is standard ATX.. never really thought of that tell i typed this..