My two are in the back holder on the front seats but I hate them there. They stretch out the holders and still hit your knees. They're a little too bulky for the console and having them loose in the very back doesn't work.
We keep all six sets in the floor compartment directly behind the 3rd seat. There is plenty of room for headphones and several other items. I didn't even know the compartment was there til I pulled up the divider partition. It's just in front of the spare tire tool compartment. (EL Model)