Help get Alpine Headphones working model SHS-N103

[Tashy]

Just purchased 2011 Ford Territory Titanium
Alpine DVD player works excellent but sound only through car Stereo
Alpine Headphones look unused, we're put in fresh batteries, light comes on and turn volume up but no sound.
Followed all instructions in manual
I've adjusted the IR transmitter to A/B and off - restarted player each time.
Remote works fine so I think this means IR transmitter is working?

Any tips would be wonderful as I'm sick of hearing kids movies booming through the car.

DVD player: Alpine 5R79 19C195 AA Mod AsyRR Ent Sys
Headphones: Alpine SHS-N103