No, you can't pair your head-unit to the TrainerRoad app.
Head-units and TrainerRoad are both receiving devices that you pair your cycling devices to during training.
TrainerRoad acts as your head unit during your indoor workouts!
Pairing devices to both TrainerRoad and your head-unit
Some athletes may wish to record their workout on TrainerRoad and a separate device, like a head unit.
If you're connecting over an ANT+ connection, you can pair your cycling equipment to both TrainerRoad and your head unit/fitness watch at the same time.
If you're pairing via a Bluetooth connection, you'll need to only connect your cycling equipment to TrainerRoad. Bluetooth equipment can only pair to a single receiving device at a time.
Check out this section of our Help Center for more information on connecting devices.