Is there a music downloading software (similar to iTunes)?

My dad has a USB that he plugs into his car which allows him to play music straight through the car. Since frostwire and limewire are dumb, I want to know if there is a software (even if he has to pay for the music now) that will allow songs to sync to the device? I tried to add songs I purchased on iTunes and tried dragging songs to the USB, but DRMs prevent that type of sharing.