Thank you very much for your feedbacks.
I am not sure what is the brand of the visor screens.... I got these from
www.mp3playerstore.com There is no joystick on them but I can turn them on and off while opened.
The second PC will do different job in my setup. yes, it will be on the network but it will be the PC for rear passengers. They will have 2 VGA touchscreens at the back (Xernacs) and will have a choice to work with regular setup (first CarPC or switch to second one (sound options will be changed too).
Also the rear PC will be more for internet browsing, watching videos and chating

MP3 will still play from the main unit..... however the option with 2 RF headsets may fix this problem as well