AFAIK There is no reason why an FM radio receiver can not be taken into a light aircraft and used for passenger entertainment. Electronic devices are known to radiate frequencies which can interfere with navigational equipment but for practical purposes on a VFR flight there seems to be no reason why you should be prevented from doing this. From recollection there are approved units which give this facility as part of the intercom set up but they are probably expensive. If you have an ADF you already have a medium wave AM receiver so can listen to Capital Gold and navigate straight to their transmitter!. I have practiced NDB approach patterns to a local radio AM transmitter in the past (in VMC with a lookout of course). Saves getting in the way of other traffic and costs somewhat less than a handful of approaches into an NDM equipped airfield.