yeah radios are far too high tech, i spent a day fannyin about fitting a radio in my S3 only to find it wasn't loud enough to be heard! (i put the speakers on the roof at the back which was the biggest problem)
for my second attempt i built a stereo power amp for my mp3 player but it would distort when you got it loud enough to hear it over the engine!! i've just got used to the thunderous rumble that a 4203 makes at speeds greater than 0.1mph now!