You might consider one of the numerous MP3 players that are out there for music unless radio is the requirement. They can fit in your pocket and use pretty much whatever earphones you like that will fit in your helmet.
Well, the android (or any) phone might give one a hard time on controlling, i.e. in the rain... whilst the buttons of a full size stereo are still somewhat accessible for fat-fingering them with gloves on and that... ;-)
Yeah...and there is that problem again... :-D...on the headset attached to your helmet...