I think SYNC only works with the supplied USB jack location with those, and not with the Kenwood USB jack. I also don't think you can tune the satellite radio or normal radio using SYNC - but I don't know that you can with the factory radio either.
It will vary by state, but it is often illegal to have a DVD screen operable in view of the driver while the vehicle is in motion. It is also illegal in many states to ground the parking brake wire as suggested. Check with state law - the biggest concern is if you have an accident and your insurance company refuses coverage of the other persons insurance company sues you b/c of this.