as many folks were interested in the mp3 approach i wanted to give an update, I fitted the stereo yesterday and also re wired in the mp3 but via the aux in on the stereo.
previously i was just using an mp3 into an amp for the music, the sound was good etc but there was just not enough power from the little mp3 player to make the music quite loud when passed thru the amp. it was very acceptable for when moored up or just idling along but when on the move there was not enough sound at cruising speeds, with an opti!!
now the stereo is fab, gives a high quality sound and it also scans 7 weather channels, it will play mp3's on the cd as well and also it will play external ipods or other mp3 players but it amplifies the sound to a very good level
stereo is an aquatic av and is around 165 and waterproof to radio type standards. very pleased with it
amp is 250w sony item and was 50 quid, speakers are jvc waterproof items for 50 quid and are 150w each and are superb, think i got them cheap! hope that helps any other thinking of blinging up with a stereo.