Here is my analysis of the case and here is how i would rule if you chose to utilize my services. (i work for tips cuz im a noob anyway)
He is imposing a cost on you by listening to loud music. You are imposing a cost on him by choosing to live near him and work at night. After examining all of the possible solutions it would appear that him putting on a pair of headphones is the least costly solution to the problem. But then again the only reason why he has to put on the headphones is because you imposed a cost on him by choosing to work at night and live near him. therefor he should wear headphones in lieu of playing music loudly but you should pay for the headphones.
also clearly music is important to this person so blue light special headphones wouldn't cut it.
Thanks
i considered that option, it seemed more costly over all though i could defiantly be wrong. If they did go with that option they should split the cost.