Support AUX audio issue

I tried running AUX on a friends radio with a port and nothing plays... I also bought a FM transmitter a iTrip that claims to work with all devices for my work car which plugs into the headphones plug of the S4 and still nothing however phone calls run through the FM transmitter... Does anyone know what the problem can be here? The app I use for music is Amazon Cloud Player it works just fine through bluetooth on my wife's car but anything with the AUX it doesn't run...

Any help would greatly be appreciated I work out of my car and I would like music that is not on the radio.
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