Well you might as well use a FM transmitter then get thoese small $10 digital radio's
U can get a FM transmitter very cheap and it will transmit 300meters if thats enough.
grab a small radio like that
then buy the ransmitter
That uses a two transistor two stage transmitter which makes sure the radio doesnt drift and outputs clear sound
mind u im in australia and these are australian things but there will be up there
and thats very cheap it cost $50 all up also cause its FM only u would pick up the reception in the warehouse plus if anyone does scan and find the music its FM they wont be thinking illegal
so good luck