Headphones, headphone amplifier, wireless and headsets, headphone jack adapters, etc. When you need a little bit of sanity from the noise or kid programs the kids are watching. Separate!
Headphones allow your passengers to listen to their movie and you as the driver can listen to music on the radio on your trip.
RADIO = No line of sight needed, works from AROUND the radio transmitter. BEST
IR LIGHT = Line of sight needed to IR (infrared) light transmitter. Most factory systems uses IR