No one seems to have thought about the acquisition of performance rights which can be a substantial amount based on the gross revenues of the sightseeing company.
Look at it another way. You could easily end the problem by:
1. Explaining the cost of performance rights for any music played during the flight would increase ticket costs, and it would be impossible to have enough channels to deal with everyone's music tastes. We do not have flights that last several hours like airliners.
2. Explaining the rules under which we fly require that passengers be enabled to hear what the pilot is saying at all times. That is for YOUR safety. Our pilots are highly trained and can land this aircraft safely in nearly all emergencies. YOUR safety requires quick action and compliance with any instructions the pilot gives. (You may prefer to leave out descriptions of auto-rotation and the need to begin that process nearly immediately on flame-out.)
Give each passenger a card explaining these issues, and perhaps have a map of the route on the card and urge the passengers to pick out certain landmarks from the route. Get them looking out the windows and watching the show there. Give statistics on the flight, tell people how the helicopter works, talk about the training required to be licensed to fly a rotary wing aircraft. Promote your other tours, promote a flying school that offers FAM flights.
This is a classic case of someone misinterpreting the problem, not unusual with people who aren't used to critical thinking. Instead of complaints about preoccupied teenagers not being able to listen to their music, the question should more accurately be, "What can we do to make the flight more interesting for younger kids who are at the 'bored with everything' stage."
A few good ideas might even come from asking kids after the flight what they would do differently. You might get some ideas that could actually work.
But to go off on crusade to find music players overlooks a bunch of better solutions. Going on a search for music players is giving up in defeat and admitting our helicopter tours are so boring that kids would rather listen to music.