Compressed music in the car sounds very detailed, as it pushes certain things forward in the mix, and you can therefore hear things easier than you can at home on a decent system... but, its not hifi.
Radio 3 is capable of stunning quality, especially on live music, but try listening to it in the car, you can't hear anything useful.
I don't use FM at home any more, as the 320bps Radio3 via the 'net, for me, is good enough, though I did listen to FM at a friends house recently, and was stunned how good it sounded via her Naim tuner and ancient 32/160 system. If I listened to Radio 3 a lot, I would probably go back to FM.